Dar gato por liebre

Literally: To give cat instead of hare

Example: “Pagué por aceite de oliva y me dieron gato por liebre.” — I paid for olive oil, and they sold me a bill of goods.

English equivalent: To sell someone a bill of goods

Origin: Selling cat for hare is passing off something cheap as something valuable. It goes back to the bad reputation of old inns, accused of serving cat stewed as rabbit or hare, and Golden Age writers such as Quevedo and Cervantes joke about the practice. A rhyme travelers were said to recite over a suspect dish has survived: si eres cabrito, mantente frito; si eres gato, salta al plato (if you're kid, stay fried; if you're cat, jump off the plate). Catalan and Portuguese have the same phrase.