There is a U.S. federal law which gives warranty of merchantability among others (not sure about E.U.).

A major store sold me an expensive item that didn't work, and the store's return policy didn't cover it, so the store said file a warranty claim with the manufacturer. I just did a credit card charge back instead, because the store has to sell me something that works.

If for whatever reason the credit card charge back didn't work, I could use the store in (small claims) court and win.

AI: "The implied warranty of merchantability is a legal guarantee that a product will function as expected for its ordinary purpose, such as a toaster toasting bread. It is automatically applied to most consumer goods sold by merchants and does not need to be in writing."