Tip - To be Sure: Ask an Unexpected Question for which the person is not prepared to Lie

According to a study by Newberry around 4% people are accomplished liars and they can do pretty well. 

You can a catch a person in his own web of lies by watching them carefully and asking them something they may not expect from you, basically which they are not prepared to answer to trip them up.

Behavior Changes and Gut Reactions will bring the truth in front of you.