По образчику узнают и сукно

We can judge of the quality of a whole thing by a little piece

Cf: By a small sample we may judge the whole piece (Am.). The sack is known by the sample (Br.). You don't have to eat a whole tub of butter to get the taste (Am.). You may know by a handful the whole sack (Br.). You may know by the handful the whole sack (Am.)