So you are thinking of a number of sellers competing for the buyer?
This would help with product discoverability since other users can suggest products the buyer had not originally thought of as well as helping the buyer to get the exact product they want.
Cheers
Like any marketplace there'll be time wasters - I don't sell on eBay anymore because of them - but in my experience, most of the time its the buyers that are time wasters.
In our case - since buyers have gone to the effort of creating a WTB listing, you could argue they're less inclined to waste sellers' time. Of course, the feedback system/reporting users would help us to identify repeat offenders and take action.
Check out our demo which should help explain things: http://www.wantobuythat.com/demo.html