I am no scientist but I don't think you can "judge a book by it's cover". Look at Ted Bundy a evil serial murder who was very handsome. Could you tell Einstein was a genius by just looking at his sloppy appearance? It is a mistake I think to try to judge someone by merely looking on the outside, not until you get to know someone can you tell who they really are. Let's not pass up a chance to find true friendship or maybe true love by making superficial judgements about the people we meet.
Looks takes a lot about someone and yes they can be used to define someone even if that not who they are. Looks are habitual patterns and character of behavior of any individual as expressed by physical and mental activities and attitudes; distinctive individual behavior of a person, considered together. You can get more information on http://reference.yourdictionary.com/word-definitions/define-personality-traits.html.