Imo, there should be a trade cap put in place based on supply/demand of a village, even if its artificial. This would provide a more realistic feel in terms of trade, but would hinder people who rely on grind-based strategies for acquiring valuables. You could also create a higher or lower demand for some items depending on the culture, I think this is already implied in some trading sequences where traders are "looking for high quality furs", however I don't know if there's an actual demand value representing that. As someone who's played many RPG's, I think however, adding a system that limits the players trading capabilities more so than expanding those capabilities will be more detrimental to the overall excitement when playing, with the exception of patching realism-breaking exploits.