Наружность обманчива Cf: Appearances are deceiving (Am.). Appearances are deceptive (Am., Br.). Judge not according to appearances (Am.). Looks are deceiving (Am.). Never judge by (from) appearances (Am., Br.). None can guess the jewel by the casket (Br.). Things are not always what they seem (Am.). You cannot judge a book by its binding (a sausage by its shin, /of/ a tree by its bark, the horse by the harness) (Br.). You cannot (can't) know the wine by the barrel (Br.). You can't tell a book by its cover (Am.)
Русско-английский словарь пословиц и поговорок. Академик.ру. 2013.