Buyers post their need for a product or service, then suppliers bid to fulfill that need. Unlike an auction, prices only move down. Free Markets (industrial parts, raw materials) uses reverse auctions as its primary market mechanism, serving large buyers. Since buyer power is key to reverse auctions, they work either for large enterprises or when practiced by intermediaries like KillerBiz andBizBuyer, which aggregate demand of many small buyers. Reverse auctions also are becoming common features of many Net markets.