How about a Wanted section? The buyer puts up the item they want and starts the auction at the highest price they are willing to pay. Bidders who can supply the goods/services bid a lower price. The lowest bid wins.
Collectors might want that one special eggcup to complete their collection. You might think the kids' parties would be improved by a dry ice machine - not worth paying normal prices, but if you could get one cheaply enough... You might want a cheap soilicitor to do your conveyancing, or the best quote for re-building your house of cards. You could advertise for weapons of mass destruction and find out who's really got them...
There are a number of things I would like to get hold of, no idea how to find them. I'd certainly use it!
By the way, you do realise that making this section public is giving away valuable ideas to other auction sites? The unmentionable one, the Voldemort of auction sites, has added several categories quite suspiciously soon after the ideas appeared here.