don't judge a book by its cover

don't judge a book by its cover

Don't base your opinion of something (or someone) on the way it (or one) looks. This report may look dull, but don't judge a book by its cover—I will have you riveted by the facts and figures in no time! I know she's a little frumpy, but don't judge a book by its cover, man!
See also: book, cover, judge