A dealer in onions is a good judge of scallions.
More French Proverbs:
He has a good pledge of the cat who has her skin.French
He who torments others does not sleep well.
French
One has always strength enough to bear the misfortunes of one's friends.
French
Give him a foot and he'll take four.
French
One barber shears another.
French
For most people love of justice is no more than the fear to suffer injustice.
French