How can you tell if someone is not telling you the truth?

I've tried checking if you ask someone a question it seems that if they look to the left it doesn't mean they lying. I also noticed sometimes they look away before giving you the answer but not sure that is proof. Last thing that may be true is that if you ask someone something and they not going to tell the truth they may just keep quiet and let you carry on talking so that they don't have to answer.

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6 mo
How accurate is intuition?
How can you tell if someone is not telling you the truth?
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