bait and switch
A deceptive commercial practice in which customers are induced to visit a store by an advertised sale item and then are told that it is out of stock or that it is far inferior to some more expensive item. For example, I won't buy a car from this outfit; they're notorious for their bait and switch tactics. The verb to bait has meant to supply a hook or trap with a morsel of food so as to attract a fish or animal since about 1300; the verb to switch has meant to change, alter, or transfer from one thing to another since the 1890s. The pairing of the two, however, dates only from the 1920s, although the practice is surely much older. It is called switch-selling in Britain.