Economists normally assume people's preferences should be

equal to her willingness to pay, the buyer would be indifferent about buying the good: If the price is exactly the same as the value she places on the album, she would be equally happy buying it or keeping her money.

To sell your album, you begin the bidding process at a low price, say, $10. Because all four buyers are willing to pay much more, the price rises quickly. The bidding stops when Taylor bids $80 (or slightly more). At this point, Carrie, Rihanna, and Gaga have all dropped out of the bidding because they are unwilling to bid any more than $80. Taylor pays you $80 and gets the album. Note that the album has gone to the buyer who values it most highly.

What benefit does Taylor receive from buying the Elvis Presley album? In a sense, Taylor has found a real bargain: She is willing to pay $100 for the album but pays only $80. We say that Taylor receives consumer surplus of $20. Consumer surplus is the amount a buyer is willing to pay for a good minus the amount the buyer actually pays for it.

Consumer surplus measures the benefit buyers receive from participating in a market. In this example, Taylor receives a $20 benefit from participating in the auction because she pays only $80 for a good she values at $100. Carrie, Rihanna, and Gaga get no consumer surplus from participating in the auction because they left without the album and without paying anything.

Now consider a somewhat different example. Suppose that you had two identical Elvis Presley albums to sell. Again, you auction them off to the four possible buyers. To keep things simple, we assume that both albums are to be sold for the same price and that no one is interested in buying more than one album. There-fore, the price rises until two buyers are left.

In this case, the bidding stops when Taylor and Carrie bid $70 (or slightly higher). At this price, Taylor and Carrie are each happy to buy an album, and Rihanna and Gaga are not willing to bid any higher. Taylor and Carrie each receive consumer surplus equal to her willingness to pay minus the price. Taylor’s consumer surplus is $30, and Carrie’s is $10. Taylor’s consumer surplus is higher now than in the previous example because she gets the same album but pays less for it. The total consumer surplus in the market is $40.