Hello, Natasha!
I heard similar expression in Russian, darennomy koniu v zuby ne smotriat.
One shouldn't look into the teeth of a horse that was given to one as a gift, right?
I think my English translation is cumbersome and too long, has to be better wording for that.
But what it means is that you should accept a gift as it is without looking and finding defects on it.
You got me here as well, I was just trying to think of my own Qazaq equivalent for this proverb......................