With accent marks:
Дарёному коню́ в зу́бы не смо́трят.
Do not look at a given horse's teeth.
In the old days, when buying horses, people determined the age of a horse by the teeth. Sometimes, having received a horse as a present, some began to complain that they were given a walking antiquity...
This Russian proverb should be understood as follows: never say that you don’t like a gift or that it is bad. This will offend the giver while he really wanted to please you. It is not polite. Be sure to day thank you. And do not forget that not everyone has the opportunity to make expensive gifts.
Other Russian proverbs
Your own shirt is closer to your body.
Don't go to the woods if afraid of wolves.
The further into the forest, the more firewood is there.
The demon is not as scary as he is depicted.
Оne sees the mote in another's eye and ignores the log in his own.
An old friend is better than two new ones.
Silent means consent.
If you like sledding, you should like to carry the sled.