What you are describing doesn't sound like a reverse auction. Maybe you are talking about one of those versions of a lottery where people bid by paying good money for a service and the lowest UNIQUE bid wins. So a valuable car maybe worth �10k is offered and people in their thousands bid a few pounds, but maybe the person that bid �21 was the only person bidding �21 so he gets the car. The promoter makes his money many times over from the dumb punters who all piled in low, and got nothing. THAT'S a lottery.