Ive tried something like this site before, and to be honest its garbage!
You buy bids (not sure on how much they are) When an item is added its got a countdown on it, say 5 minutes for example. So you'd place your bid, then the timer resets back to 5 minutes, then someone else puts a bid in after you, and the timer goes back. This goes on for ages, until no one else bids, so the last bidder wins. So although you might end up buying the item for £30, its actually cost you an extra £50 for the bids
I hope that makes sense, it is hard to explain in writing, but Id try and stay clear!