All RPG's like Skyrim, Risen, Gothic have similar trading system. You have price for something and that's it. Gothic 3 was little bit more complicated and all traders have some amount of gold so you can change things directly by it price.
Some days ago I've decided to sold my not worked stuff at the market. When I came here they asked me what is your price ? And it was little challenge cuz I have no idea how much does it cost. So if my price was too big they say no and probably don't want to continue trading. Of course I don't want to sell them too chip. So the price should be little more bigger for what I suppose to sold cuz I need to range to trade.
What if make trading system exactly like this in RPG. And of course leave old system for stores and make this system for markets.