Don’t look a gift horse in the mouth!

A saying when someone gives you something useful but you don't like it at all and you would like to have something better for you .

In the past, when buying a horse, people looked to see if it had healthy teeth.

Dad: „I will give you my little car for your birthday.“
Daughter: „But I don’t like it! I’d rather like a big car!“
Dad: „OH, c’mon! Don’t look a gift horse in the mouth!“