A caval donato non si guarda in bocca *
* Don’t look in the mouth of a gift horse
Expression used here and there by Almost Everyone
It means that all that is given is something gained and it would be impolite to comment on the quality of the gift.
"La maglia che ti ha regalato Giuseppina non è di buona qualità, ma a caval donato non si guarda in bocca."
"The shirt Giuseppina got you is not of good quality, but don't look in the mouth of a gift horse."
Added August 2020 by mattia
7 out of 8 Italian speakers have heard this