Yesterday I posted about monster bits.
One of my players pointed out that you can basically sell all sorts of animal bits, real-world. Of course, that's partly what I'm trying to simulate. That's why I added a rule that potentially adds value to those random bits, instead of using the existing DF pricing of "no one wants it, it's valueless." There is a chance people will buy anything.
A chance, though, not a certainty. It's a pre-modern market, not a post-internet connected world. You need to find a local buyer at the time you are selling. That buyer needs to think they can sell it right away. This transaction needs to be done quickly because we're not playing Warehouses & Wharves, so people aren't storing materials and shipping them to buyers elsewhere. We're not playing shopkeepers either, so you're selling to the merchant who sells to the merchant who sells to the end-users, and if you're lucky one of the members of that chain is missing and you get a little bit more.
Pricing is pretty low, though. This makes sense given the DF economy. $1000 equips a new delver. $600 buys a sword, and $40 a weapon-grade axe or a spear. $5000 adds magical damage to a sword, being raised from the dead is $15K! Prices are bound to be low for mundane anything.
Plus even if it's unusual (dragon bits, say, or the horn of a rare purple gargoyle, or bits of rock troll), it's not necessarily very valuable. Rare monster bits rarely top $500, and more often are in the $100 or $1dx100 range, and that's intact, properly harvested, and fresh. Dragons top out in the near-$5000 range, for big ones, and that's a magical creature with parts that can do many things for NPCs in town.
It also needs to be identifiable and attractive. Broken bits of random bones, teeth pulled out of a critter not identifiable post-pull, pelts that don't look any different form other pelts, etc. aren't going to have a lot of value. You can lie, but people lie all of the time, and that depresses the market value as confidence men and profiteers pile on.
Damage to the monster doesn't help. Delvers generally inflict a lot of damage to win the fight, and more gaining the bits. It's not going to ensure a salable piece of monster at the end of it, even if it started out as valuable.
It's also a buyer's market. You, the delver, need a buyer at the time you are selling due to your own need to move the stuff now because it'll spoil. Horns, etc. won't, but not every horn is useful and not every horn is attractive and valuable. Teeth are great for collections and savage fetishes, but I work on the assumption that "collectors" don't generally exist. Alchemists and demonologists and wizards who need bits do, but mostly people aren't putting together vast collections of monster bits, rare coins, and so on just to do so. Price depends on utility.
Another thing is that these things are relatively common. For all that squirrel tails* and otter's noses might be salable, if you're pulling lots of the same items out of a dungeon or from the local wood nearby, it's a local commodity. Seashells sell for less by the seashore** and firewood sells for less in the forest.
On top of all of this, part of it is the fun aspect. I'm totally amused by PCs stripping dungeons down to the wall fixtures. But "now we cut the monster into salable bits and arrange encumbrance to bring it home to sell" is not as much fun to me as "we open the chest and take the silver and gold and magical items." The DF economy nicely makes the latter much better than the former. If it didn't, then the game really should center on trapping monsters and killing them efficiently and with the least damage to their body parts, then harvesting and selling them. You can do some of that, and taking the special spleen of the cave slink is worth doing, but the game doesn't focus mainly on selling owlbear meat.
I want to reward my players for their enterprise, but it'll skew the game if every monster is effectively a pile of loot, and if monster pelts are the way you make a profit. That takes us right back to "farm for XP" instead of "delve into the megadungeon and tell gaming stories for years about the challenges you faced."
I figure scrap-based rules do that nicely.
* Mepps used to have price lists in their catalogs for buying animal tails for their lures.
** Tourist shops notwithstanding - you need a tourism-based economy before anyone is buying shells to avoid finding one for free.