Researchers have discovered that surprisingly small factors - where we meet someone, whether their posture mimics ours, even the slope of their eyebrows or the thickness of their chin - can matter as much or more than what they say about themselves. We size up someone's trustworthiness within milliseconds of meeting them, and while we can revise our first impression, there are powerful psychological tendencies that often prevent us from doing so - tendencies that apply even more strongly if we've grown close.

Very interesting read.

I think that looks are a part of it but I've noticed more than anything it's what they say and how they say it. They're what I call smooth talkers.