You can't judge a book by its cover.
你不可以貌取人！
Angela： "He dresses in plain clothes and drives an old car. Who would know he is the richest man in town？"
Andy： "You can't judge a book by its cover."
安吉拉：他穿着很平常，开着一辆旧车，谁会想到他是这个城里最富有的人呢？
安 迪：你不可以貌取人。
You can't judge a book by its cover means that before you can judge something， you need to take a deeper， closer look at it.
中文意思：你不可以貌取人。
you said right. 