How about both systems? Being able to trade as is already possible, as well as having some sort of auction thing. This way you could buy items with gold or trade items for gold or other items.
@The poster above me: I think something in the middle would be best, instead of going from one extreme to the other (gold being really easy to find a la D2, and gold being so rare people pay real money for it). Having a good balance, where gold is easish- but no way near as easy as D2. It would give Gold an in-game value but still not much of a real-world value.
I can't even try to think up a way to solve the problem as I haven't had much experience with the issue. All I can do is make suggestions on what I read here in the forums.