Last time I checked, the mishna in Avos discussed this issue…..
AL TISTAKEIL B’KANKAN, ELAH B’MAH SH’YESH BOI” (Do not judge the jug, only by whats inside it)
L’havdil, they have a similar saying in English…..
“Never judge a book by its cover”
(Yes I know people are not books – so please dont reply in that vain!)