bait and switch
n. a dishonest sales practice in which a business advertises a bargain price for an item in order to draw customers into the store 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. Electronic items such as stereos, televisions, or telephones are favorites, but there are also loan interest rates which turn out to be only for short term or low maximums, and then the switch is to a more expensive loan. In most states this practice is a crime and can also be the basis for a personal lawsuit if damages can be proved. The business using "bait and switch" is an apt target for a class action since there are many customers but each transaction scarcely warrants the costs of a separate suit.