I somewhat believe in it. But not as straightforwardly as you describe it. I mean, we all see someone is happy when a big smile shows on their face. Then, slightly more difficult to put in exact words, many of us can tell a fake smile from a real smile… The mouth may still be smiling, but the rest of the face doesn’t play along. Some may be fooled by the fake smile. So this is something you can be better/worse at. Just as some may have trouble recognizing the expressions, others may notice subtleties that many would not. I am not sure whether or where an absolute limit to this ability could be. Some good friends barely need to speak to tell what the other is thinking. Of course, their shared context (history) makes all the difference.
No I don’t. Some aspects of when people lie can be detected through body language/facial expressions. But even lie detecting is flawed. I think you never know what people are really thinking.