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Sure, but if you are keen, wise , and experienced, you can nearly always tell the difference. Practice with it, and you will get better at reading people. Not to the point where thy think you are weird, just gaze slighly longer than usual, or at least look people in the eye when you speak to them.

Besides, that is the point. If you need to know whether someone is telling the truth or not, that would be an instance where the risk of making a truth teller slightlyuncomfortable is worth the reward of finding out if they are indeed telling the truth. This is a technique for only infrequent, important situations.