[Baram]

Remove the ability for NPC owned shops to purchase items. Now player crafters need to own a shop, sell directly to a player, or supply another players shop with goods. This is basically how it is in the IRE games, and I always had fun as a merchant. Even without any trade skills of my own I'd buy some things at the best price I could, barter them up to better things, sell those for a nice profit to a player, buy something else... until I was supplying shops (still with no crafting abilities of my own), and then got my own shops.

You also want to factor in what things can come from "mob drops" to make sure they aren't better than player made things (in general). An easy way is to make it so player made have a high "max" stat, and always a high "decay time" than mob dropped items.