According to an excellent Boston Globe article by Drake Bennett, your face dictates your perceived trustworthiness. Princeton psychologists have found that even when a person’s features are expressionless, certain people seem more trustworthy than others. Social psychologist Susan Fiske says, "Trustworthiness is the very first thing that we decide about a person, and once we've decided, we do all kinds of elaborate gymnastics to believe in people." Or to disbelieve in them.
It’s not just the face, either. Work by scientists at Duke and Stanford shows that if a person imitates your body language while talking to you, they seem more honest.
Considering my favorite pose, it's no wonder I always loved this guy!