Como dizer "Comprar gato por lebre" em inglês

Comprar (comer, vender) gato por lebre.

To buy (sell) a pig in a poke.
To sell a pup (or buy a pup).

The idioms pig in a poke and sell a pup (or buy a pup) refer to a confidence trick originating in the Late Middle Ages, when meat was scarce, but cats and dogs (puppies) were not. The idiom pig in a poke can also simply refer to someone buying a low-quality pig in a bag because he or she did not carefully check what was in the bag.
Wikipedia

As expressões referem-se a um truque de vigaristas que originou-se no final da idade média, quando a carne de gado era escassa, mas gatos e cachorros (filhotes) não...