bait-and-switch

Bait-and-switch is a form of fraud used in retail sales but also employed in other contexts. First, the merchant "baits" the customer by advertising a product or service at a low price; then when the customer goes to purchase the item, they discover that it is unavailable, and the merchant pressures them instead to purchase a similar but more expensive product ("switching").

Bait-and-switch techniques have a long and widespread history as a part of commercial culture. Many variations on the bait-and-switch appear, for example, in China's earliest book of stories about fraud, Zhang Yingyu's The Book of Swindles (c. 1617).