What is a primary feature of a 'sealed bid auction'?

In a sealed bid auction, bidders submit their offers confidentially, which means that no participant knows the amount of the bids made by others until the auction is concluded. This confidentiality creates a competitive environment where bidders are encouraged to submit their best possible offers, knowing that their bids will not influence or be influenced by others during the bidding process. The goal is to maximize the value of the bid without competitors adjusting their offers based on the visibility of others' actions.

The other options highlight characteristics that do not pertain to sealed bid auctions. In contrast to a sealed bid auction, public bidding allows all participants to see the bids as they are made. The role of the auctioneer in a sealed bid auction does not include adjusting bids; instead, it is focused on collecting and eventually revealing the bids. Lastly, in a sealed bid auction, bids are not announced immediately; they remain confidential until the predetermined time for their opening.