I'm trying to work out the best way for players to sell things to NPC shopkeepers. I've never particularly like the traditional shopkeeper model that is willing to buy virtually anything that the player can pull out of their bag, even if they don't (or won't) sell it. I've considered having shopkeepers only buy the things they sell, or only have a finite list of things that they'll buy, but I guess I'm undecided as to what the best way to go about a shopkeeper is.
Is it worth deviating from the standard model? I don't particularly like it, but I realize that it is, after all, a game, which is meant to be fun and playable, rather than realistic or artistic.