I would still have a few concerns though, this would probably bring excessive complexity to the AH, because for example, if you are a seller, you are probably going to end up doing some extra work, not only you will have to check the current AH prices from other sellers (competitors), but you would also check the buyers offers against one another and against the current sellers prices in order to find the option that would benefit you the most.
just to chip in, Runescape has a great auction house, system called the great exchange.
basicly, you go to an NPC, type in what item you are after in a search box, it will auto fill with results.
When you have picked an item, you see a price on it, the market price, take your Fight Club
as an example. the market price is 1337 gold for it. So the buyers / seller value is automatically put to match that market price, now the buyer / seller can either up or lower the price. By a set value or in 5% increasements.
If you wannt something to sell fast you lower your sell price under the market value, and if you wanna sell high put it at a slighly higher price.
So how does this work:
Player A: puts Fight Club
on the AH, for 1337 gold
Player B: wannts to buy a Fight Club
but he wants it quick, so he types in he is ready to pay up to 1500 gold for it.
now as we have a Fight Club
up for 1337 gold on AH, Player B will win the club. but he will only pay 1337 gold and get 173 gold back. and everyone is happy,
market values is calculated after the items sells. its kinda hard to explain it, should be some great guides on how runescapes grand exchange works some place on the web.