bait and switch

Definition from Nolo’s Plain-English Law Dictionary

A dishonest sales practice in which a business advertises a bargain price for an item in order to draw customers in and then tells the prospective buyer that the advertised item is of poor quality or no longer available and attempts to switch the customer to a more expensive product. In most states this practice is a crime and can also be the basis for a personal lawsuit if damages can be proved.

Definition provided by Nolo’s Plain-English Law Dictionary.