There is a raft of research and information available about this question, but one need not look further than this lecture by Pamela Meyer to get a good handle on the answer.
I’m no expert, and so instead will try and answer how I know when someone is lying.
Short answer: I don’t know. Not really.
But if I really had to try and figure it out, I would say a combination of body language and, most importantly, a focus on the individual’s eyes. The eyes cannot lie.
When you ask a colleague, or an acquaintance, or anyone that’s not a very close friend “How are you doing?” and they respond “Good” or “Fine”. A lot of the time that might be a lie too. Nobody’s fine. Todos están jodidos.