lemon law

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A law obligating a motor vehicle manufacturer or dealer to refund to a purchaser of a vehicle the full purchase price, or to offer a replacement acceptable to the purchaser, when the purchased vehicle proves to have substantial defects that cannot be repaired after a reasonable number of attempts.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun law, idiomatic A law dealing with defective items, especially automobiles, and consumers' rights.