According to the Hotwire website, they deal with brand-name travel companies exclusively. This strategy allows Hotwire partners to clear out their supply and sell inventory that would otherwise go unsold. Hotwire reveals the prices and the travel dates of all their products upfront and does not sell via a "bidding" or "auction" model.
The Hotwire website emphasizes their partnership with well-known travel companies and their strategy of selling discounted inventory through transparent pricing and readily available dates.  They avoid traditional bidding or auction methods.