They are in the business of protection, so they are taught to scan crowds for someone looking differently, hence they are astute in reading nonverbal clues. Also, they investigate threats against public officials and have to determine whether the person is unbalanced or a real threat. This is a more nuanced decision than merely saying innocent or guilty. They have had very good training on these issues for many years. The CIA has had heavy reliance on polygraph rather than human decoding.
Men exaggerate their money, their accomplishments and their willingness to commit.
Women use makeup and clothes to look better than they 'really' are and act more excited and captivated by the men than they really are. For example, in poker, with salesmen, politicians, etc., there is some expectation of glossing over. Similarly, we expect people to be on their best behavior early in dating relationships. We expect things to get worse, so if people don't dress, don't act nicely, we assume it is downhill from there. One could argue that dressing up, using makeup or working out are 'lies,' but they are also signs of respect and caring for yourself and others.