I think there should be a poster board system such as

Built is looking for a dark watch sword (any level) for (200k)
Said player looks on the board
Wound is looking to sell their dark watch sword lv21 for 250k but see's builds offer and sells

Of course there will be a taxing system like always

Then again it would that's what forums is for and there will always been that one player that will have a problem with it.

There will always be problems and stipulations to any buying/selling/bidding systems.

Although I do like your idea Mohok