What is the meaning of [Appearances are deceptive]

Do not judge a thing by its appearance. As another proverb reminds us, All
that glitters is not gold.

> Why did you believe him? Why he said he wasn’t married? Asked Mary.

> Because, replied Pamela, he was so good-looking and well-dressed, and had
such a nice voice.

> All that glitters is not gold, Mary reminded her.