Which of the following is NOT a type of auction?

The correct answer indicates that a reverse auction is not classified as a traditional auction type, as it operates differently from the others listed. In an English auction, participants bid openly against one another, with the highest bidder winning the item. A sealed-bid auction involves competitors submitting hidden bids, with the highest bid winning after all bids are revealed. A Vickrey auction, which is a type of sealed-bid auction, involves bidders submitting bids without knowing others' submissions, and the highest bidder wins but pays the price of the second-highest bid.

In contrast, a reverse auction flips the traditional auction format. In a reverse auction, suppliers compete to provide goods or services, and typically the price goes down as the suppliers bid against each other to win the business. This model is particularly common in procurement contexts where buyers seek to lower costs.

Therefore, while the other options represent conventional auction formats focused on selling to participants, the reverse auction presents an entirely different approach centered on buyers inviting suppliers to compete. This understanding of auction types allows participants to recognize the distinctions in auction mechanics and applications.