as far as the infinite number of skins and gems

Skins are used in EVERYTHING in a feudal society. Leather armor, leather pouches, leather harnesses.etc. I'd be willling to bet that the furrier and tanner have big contracts with the city to churn out as many raw and prepared skins as possible for the guards armor/backpacks/sheaths/scabbards also with the merchants for the leather harnesses that are used on the beasts of burden, with the innkeeps for waterskins and wineskins, with the empaths for leather curtains, with the bards for specialty tanned skins for instruments...and the list goes on. Remember it's not just the PCs allegedly buying this stuff it's the unseen peasants as well and the unseen noility.

Gems can be used in many ways also Jewelry, cutting of gems and stone, adornenment on buildings....maybe in the crafting of magical items and certainly in trade goods.

The Big problem I have is that weapons and shields should pawn for more as they can be broken down to make more weapons and shields or resold cheaply at the pawnshop. Having Shard as the only place you can buy previously owned items bugs me a lot.

Also I really want to be able to take MY gem into the jewelry store and have them set it into a setting. Take my stunning sapphire and my animite and give them to the lady in Aesery to get an animite athlomi inlaid with stunning sapphire....
There is no way for people to buy the rare gems that the gemstores are taking in. Much sadness.