It would be a bit of doing on the GMs part, but just as a though, its it harder to have NPCs for sale? By this I mean, players either buy or rent NPCs in the game. Each player can then trade items to this merchant, and set prices. This way all trading would be done in game, with or without clients online. Possible issues with this though would be lag if say, 300 "merchants" were being placed in the bazaar...but I've no real clue as to how much lag one standing NPC could generate. Just a thought though...but if thats going to have a lot of issues and or become far to complex, your idea sounds awesome just as well.
