We are told not to judge people by their appearance. There are sayings like "Appearances are deceitful" or "Don't judge a book by its cover". But let me ask you what is the first thing that we do when we meet a new person? We judge! Some people immediately attract our attention and some make us look away.
I think judging someone by their appearance is our human instinct, a survival instinct. For example, if I got lost somewhere and needed to ask for directions and there were two people to choose from: a guy with lots of piercings and tattoos or a man wearing a suit and a pair of glasses, I would probably go for the man in the suit.
In fact it isn't bad to judge someone by their appearance, if you are able to give that person a chance to show their inner world. We should always be open to the possibility that our first judgment could be wrong.