Cut off their tusks

Fortunately, trolls have tusks. Cutting the end off of tusks takes a bit of work, but there is no blood involved, so it is suitable even for the squeamish.

Note, horns are keratin over bone. Tusks are overgrown teeth. Troll tusks won't bleed.

Fine, Strip them and Bring their crotch straps back

-Trolls wear loin clothes at least

-Trolls aren't hygienic so it would be hard to forge multiple used troll crotch straps

-So if they really press whether they are real or not you can tell the NPC to smell them and find out.

Get hold of a couple of palantirs palantiri. The NPC can watch the live action.

Necromancy

Why cut off a ear when you can kill two trolls with one spell? You could get your hands dirty cutting off ears, and the quest giver might still suspect you made fake ears. It'd take a brave person to accuse you of making 15 fake zombie trolls. Even if the contract requires you to remove the ears (and you are the lawful sort), you could keep your own hands clean and just get your zombie minions to remove each other's ears. If after all that they still refuse to pay... well then you have 16 pet zombies. It is win-win!

Assert you did.

Thrash up your stuff and bloody your sword. Go back to the dude. Yell "I KILLED TROLLLLLS!" Let the residual battle frenzy gleam in your eye. Make sure he understands you have suffered much brain damage from many fights over your life, but if anything that has increased your 99 strength.

If he starts laying conditions and caveats on you, become angry. If he says you did not follow the instructions, show him the blood on your weapons and yell about trolls.

He will offer you half pay to leave and not come back. He will apologetically explain he needed the troll parts which is why it is just half pay, but he feels bad about wasting your time. Take the money in exchange for him conceding that you killed the trolls. Give him a tip with his own money for saying it.

DOCUMENTATION

All your main char has to do is bring a vial of ink with him/her and also a sheet of paper (hopefully a journal). Assuming your character has the literacy skill > 10, they should be able to read and write.

After your character has slain the trolls, have the character take out some ink and a sheet of paper. Spread the ink over the troll hand and ear. Attach the sheet of paper to the hand and then the ear. The ink marks from hand/ears should be unique to each troll. Now present your slaying documentation to your quest giver and bing bang boom LEVEL UP!

Ear Wax

Troll Earwax is the best wax for clean burning candles. Your quest is not simply to go kill these trolls but to harvest their earwax. You are paid by the weight of wax brought back that way fair compensation goes for bigger trolls with more wax than the smaller trolls who just don't make enough yet.

Take along an agreed credible witness to document the activity.

Perhaps a priest or other literate person.

Does create the extra bother of protecting them.

Burn the Body, then bring back the skull.

The squeamish adventurers kill the troll via boredom.

No blood, no guts, nothing.

The adventure pays (on account of being squeamish) individuals without a sense of smell to carry/drag/transport the full troll body back in an ice bag.

• The guild must acknowledge that it is indeed a dead troll, no questions asked.


• The adventurer is renowned for their ability to slay otherwise quite difficult to kill trolls without actually laying a hand on them.


• The DM buys shares in the ice business because it's going to be big.

Collect their foreskins.

David was tasked by Saul to collect a dowry of 100 Philistine deaths. David, one of life's over-achievers, returned with proof of their deaths in the form of 200 of the offending articles.

Therefore David arose and went, he and his men, and slew of the
Philistines two hundred men; and David brought their foreskins, and
they gave them in full number to the king, that he might be the king's
son-in-law. And Saul gave him Michal his daughter as his wife.

_{^{1 Samuel 18:27}}

Not only was it super-effective in proving their deaths (since no respecting Philistine would allow David's small army to mess with their junk if they could possibly help it) but it was both portable and relatively non-bloody because a dead body has practically no bloodflow.

If your men are genuinely squeamish about even a single drop of blood they can use the local equivalent of cautery by heating a razor-sharp knife over a flame until red hot. This will seal the blood vessels as they cut.

Make a travois! They're certainly simpler to make than anything with wheels

Regardless of your power level, dragging is easier than carrying. Travois don't require wheels, though it's certainly an option to reduce your expended effort. Make it longer, or tie a rope to it if you're still getting nauseous. Regardless, it's a simple enough device that you can hook it up to a horse or an unenthusiastic hireling

That being said, a cart or wagon will serve you better, but that's less outside-the-box

You see hiring a guy to kill 15 troll and not telling them how he should prove those 15 kills would be the stupidest idea ever. Why?

Because person who take a quest to kill 15 troll IS the person who will drag (or will hire other people to drag) 15 rotting, smelly, troll carcasses to your doors to prove that they, in fact, killed them. And to prove that those are their kill, and not some roadkills they find lying around, they will either catch souls of those trolls to testify before you who slayed them or will have you watch their death with some magic.

Great deal, now you have 15 rotting meatbags, 15 screaming souls or you watched so many troll death you have it imprinted in your eyeballs and one person who you need to pay because you see they are nothing to flick around.

You know what is better? That don't have blood? That don't require you to watch? And will have higher crop with the same bounty? Troll Jewellery. Let's say that troll wears rings. They have finite amount of fingers so you assume that every troll can wear 10 of them. So you say "hey, bring me 150 troll rings".

The catch is that not every troll wear 10 rings. Some wear 3, some wear none. The result is that to get 150 rings adventurers need to kill much more. Yet the guild pay like they would kill 15 of them.
EXTRA CATCH FOR MAXIMUM EXTRA MEGA PROFIT The guild, and trolls, are the only ones who can melt those ring into "non-troll, not at all, all genuine dwarf" jewellery. So you make those rings worthless outside guild quest while fetching extra money. Basically the quest pay for itself while making extra income for the guild.

And this is the story of how make money in fantasy world using cheap labour and monopolizing market.

If you're really going with World of Warcraft (or D&D) style trolls, you've got a problem: They regenerate:

Although enough physical damage will kill them, trolls can regenerate lost limbs and heal grievous physical injuries at an accelerated rate, giving them a large advantage in battle.

So your proof is going to have to be something that doesn't regenerate. If you choose ears, or tusks, or fingers, or hands, or feet, your adventurers don't need to kill 15 trolls, they can capture just one, then harvest it for the relevant body part over and over (in both D&D and WoW, troll regeneration from nearly dead to unharmed occurs in the space of a few minutes at most, so you could harvest 15 trolls worth of body parts in the space of an hour, give or take).

So you need something that won't regenerate and can be uniquely associated with a single troll.

Unfortunately, the obvious solution here (in terms of maximum proof for minimum "amount of troll") is scalps; sure, the scalp itself can regenerate, but the hair is dead, and presumably grows at a relatively normal rate; you could harvest scalps over and over, but scalp #2 and onwards wouldn't have hair. The reason I say "unfortunately" is that nothing bleeds like a scalp wound and your adventurers are squeamish. As others have suggested, once the troll is dead, you could just wait a bit and the blood should coagulate, but if they don't want to deal with blood at all, they're stuck. Claws might also work (though in most depictions of trolls, a chopped off arm grows back with claws, so they may not be made of dead material the way human fingernails are).

The best I can come up with is having them collect the hair itself. It's not perfect; trolls have wildly varying amounts of, and growth patterns for, hair in most depictions, so it might be possible to take hair from one troll and pretend it came from two or more. But it's the best you're likely to come up with shy of dragging all 15 corpses back with you.

Ear wax, as mentioned in another answer, might also be viable (presumably carving out an ear and having it regrow won't have it regrow complete with ear wax build up), though as that answer notes, it can't give an accurate kill count, just a rough estimate (it's like hair, but even easier to subdivide).

There is a flaw with all of these methods: If trolls are smart, they might try to game your troll death metrics by regular grooming; shaving their heads, carving out the inner skin of their own ears (or use q-tips, whatever) every week or so, etc. If you're adventurers looking to make a buck, taking the risk of death fighting trolls that you won't be paid for might seem like a bad deal.

Bring full body vids including yourself knifing thru the heart & slitting throat of the orc, pre or post-mortem, along with an accompanying dna swab. He checks.

That should do the trick.

Get a referee / mentor to join your quest.

You may bring 15 troll ears, 20 tusks and 1 gallon of ear wax BUT:

Was it really you who did the work, or did you buy yourself through a gift shop down the street or worse, did you let others do the dirty work?

This is why the Guild of of Adventurers Anonymous provides a referee or a mentor for every one who goes on such an honorable quest of slaying innocent trolls.

The referee writes down every troll you killed and even how you killed them, because there are more than one way to kill a troll and not all of them are favoured by your guild.

Get the trolls to chase you

1. Place the NPC at the top of a safe tower or other natural defence.




2. Dig a ditch of spikes and cover with branches and leaves. Leave one place where it's easy for you to cross but make sure it looks no different from the rest of the concealed ditch apart from an odd shaped branch.




3. Find a band of trolls.




4. Get them to chase you.




5. Keep shouting insults to enrage them but run just fast enough to keep ahead.




6. Run until you get to where the NPC is waiting.




7. Cross the concealed spiked ditch, turn to face the oncoming horde and shout your worst insults whilst making rude hand-gestures.




8. Watch as the trolls fall into the ditch and impale themselves.




9. Kill any that manage to cross the narrow concealed bridge by knocking them off it in the manner of Little John and Robin Hood. Shoot stragglers who didn't quite reach the ditch with your bow.




10. Collect your reward.

This also has the advantage of being re-usable. Make sure no-one lives to tell the tale and you can use the same trick repeatedly.

Do your trolls live in caves?

1. Wait until the troll goes to sleep after a long day of pillaging villages and farmsteads. *(Usually an adventurer's first instinct is to swoop-in and save the day before another village gets looted, but you have to remember to be patient here)




2. Roll a giant bolder to the cave entrance. Make sure it's properly secured so the troll can't get out. (Maybe bring some mortar with you just in case...)

3. Wait a year and then come back to the cave. By this time the troll should have run out of food in the cave and starved to death.




4. You now have an intact troll body (or more if he had a wife and kids in the cave), with body-parts that you can say came from multiple trolls, you've also got troll weapons and troll clothes as further proof for whatever you want.

1. Help my cute elf! You must be female elf. I am sure there will be army of ready help.


2. Photo - No magic selfies or too expensive?


3. In name of my honor! Trolls are no more! Magic and divine oaths.


4. For for reasonable pay, guild verifies kills: sending extra with you or after job is done, while your pay is pending.


5. Get troll weapons or whatever your trolls have. Poor trolls.

Depends on your way of killing the trolls without blood, But if there is no modern technology around and going livestream while killing trolls is not possible, then let the troll come to you.

1) Lure the troll near the town

2) Kill the troll

3) Get Rewarded

All of the above answers(skinning the troll, ripping parts of the troll, etc..) could be bypassed by just either waiting for a troll to die, or searching for a dead troll, or making trolls fight each other, take the token and present it. My approach will make sure YOU did it, and the whole town witnessed you kill the trolls.

How you do it without blood is way beyond me, I cant seem to picture killing something without blood.

Take their Mojo

Adult trolls (or at least, the Warcraft variety) have their own special form of magic (Voodoo in Warcraft terms) that requires a special bag of charms (A liquid in Warcraft), called a Mojo. A troll will never willingly part with their Mojo while they are alive, and all trolls carry Mojo, so there is a one to one relationship between a Mojo and a troll. It doesn't require any severing of limbs, nor cutting of body parts to harvest, and it's relatively easy to carry. It's also hard to make a forgery, because it's infused with the troll's personal Voodoo magic.

Troll Semen

With genocidal adventurers constantly picking off trolls to improve their status in society it would be necessary for societies to engage in conservational efforts to stabilize the troll populations.

Seeing as how there are adventurers who do not wish to return traditional socially rewarding trophies they can be used to instead return materials useful in conservation efforts.

Using a syringe an adventurer could harvest the eggs or semen from dead trolls. Because they are dead their blood flow has stopped so sticking them with a needle will not result in any significant spray that could get on them.

The eggs and semen could then be used to artificially impregnate captive trolls thereby replacing their population.

Livestream it.

Since you didn’t mention anything about your world I’m going to assume a similar world to ours. If it is a less technologically advanced world then figure out a magic livestream that people can watch in some specifically built theater.

You’re an adventurer with the equivalence of a live gaming Youtube stream. Thousands of peasants watch you (and others) ridding the world of those pesky trolls. Sometimes the adventurers die horribly in the process, which makes it even more entertaining.

Insurance. No really.

Where there is money exchanging hands, there is risk. Where there is risk and money exchanging hands, there is always someone looking to make money from this.

Have your reward payers set the value of killed troll through investment from those who wish to see the trolls gone. Have this value be underwritten by insurers. Only troll kills which can be verified by an agent of the underwriters will count. This causes the troll hunters to pay to bring along a verified agent of the insurance agency. This Agent also collects a salary based on how few trolls are killed.

If he lies by reducing the number, he can rest assured the next troll hunt will either see him not being brought along or being used as "accidental" bait. If he lies by increasing the number, he will be paid less in his salary. Finding this value to reduce the chance of bribery is a big part of insurance.

If he tells the truth, the troll hunters are happy that he isn't taking money away from them. The insurance company is happy because their books balance. And the investors are happy because there are less trolls running around.

Edit: Also forgot that the same insurers will be offering life insurance policies and workmen's compensation options to the troll hunters. Heck, they can even offer insurance for poor hunting years.

Let's assume that an ear is enough proof you've killed a troll. Your adventures could just hire an NPC who waits till the fight is over, then cuts off the ears of the dead trolls and put them into a chest, half filled with sand (the sand will keep any blood from dripping out of the box). Then all the adventurers need to do is present the chest to whoever asked for 15 trolls.

Of course, if the adventurers have a DEX above 6, it shouldn't be too hard for them to cut of ears without getting blood on them.

I'm far more interested how they plan to kill 15 trolls without getting blood on them.

Bury the dead trolls by anthills, termite mounds, or other scavenger insects. Come back in a year or so when the trollskull is clean and hand that in.

Alternatively, boil the trolls, the trollflesh will fall right off, again you get clean skulls and bones, as well as rendered trollfat and other usable parts.

Maybe a bit stinky though, if you're not gonna clean the bodies before boiling. You'll be basically boiling the bodies in a vat of trollcrap.