I don't think it's reliable to judge a person by the first glance.
Firstly, appearance doesn't represent all.
The information of a person you can get from a glance is very limited.
You can't tell many things just from the appearance, such as the past, hobbies, eating habits and so on.
Furthermore, appearance lies, it may trick you.
What you can get is partial, which may even lead to prejudice.
A person who dresses decently and talks sincerely doesn't imply that he's definitely innocent and kind.
You can't judge a book by its cover.
So I support that one shouldn't judge a person just from the appearance.