 The two are primarily used by sellers to determine the auction type that maximizes the expected price.This optimal auction format is defined such that the item will be offered to the bidder with the highest valuation at a price equal to their valuation, but the seller will refuse to sell the item if they expect that all of the bidders' valuations of the item are less than their own.Relaxing each of the four main assumptions of the benchmark model yields auction formats with unique characteristics