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
Repetition is the mother of learning.
All is well that ends well.
The apple never falls far from the tree.
Being a guest is good, but being at home is better.
Each sandpiper praises its swamp.
To live a life is not the same (not as easy) as to go through a field.
Appetite comes with eating.
A well-fed man does not understand a starving one.