Seller announces reserve price or some low opening bid. Bidding increases progressively until demand falls. Winning bidder pays highest valuation. Bidder may re-assess evaluation during auction. Dutch, or descending-price.
Seller announces very high opening bid.
Bid is lowered progressively until demand rises to match supply. First-price, sealed bid. Known as discriminatory auction when multiple items are being auctions. Bids submitted in written form with no knowledge of bids of others. Winner pays the exact amound he bid.