του χαρίζανε γάιδαρο και τον κοίταγε στα δόντια → don't look a gift horse in the mouth, look a gift horse in the mouth, beggars can't be choosers

[spiros]

Του χαρίζανε γάιδαρο και τον κοίταγε στα δόντια → Don't look a gift horse in the mouth

You are looking a gift horse in the mouth when you receive a gift and then you question the value of that gift. Example: "This shirt you gave me is not my favorite brand." Reply: "Don't look a gift horse in the mouth! That was the best they had."
http://www.goenglish.com/DontLookAGiftHorseInTheMouth.asp

[crystal]

Beggars can't be choosers.
Prov. If someone gives you something you asked for, you should not complain about what you get. I asked Joe to lend me his bicycle, and he sent me this old, rusty one. But beggars can't be choosers. Jill: Let me wear your green dress; I don't like the blue one you lent me. Jane: Beggars can't be choosers.
Beggars can't be choosers - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.