I've seen some shards that have an auctioneer chilling out by the bank. It works pretty much like e-bay. you put an item up, determine how long the auction runs. you can set a reserve and buy now option if you want.
The auctioneer can either charge a fee to place the item up fr sale and/or take a cut of the the final sale price.
There could also be a limit of say 5 auctions actions active per account. This would insure that the auction was used in addition to and not instead of vendors already in game.
In addition to the item and any stats it may have the buyers would be able to see the highest bid, if the reserve is met(not how much it was) and time remaining on auction, as well as how much the buy now is.
This would allow people with high end items to sell get exposure with out paying an arm and a leg for vendor fees. It would also help newer people gauge what kind of items are out there to be found and how much they go for.