1. Look for anything unusual
When dealing with someone you already know, any signs of unusual voice tone, temper and awkward movements should put you on edge about the credibility of the information your are receiving.
2. Look out for stress
People who are not habitual lairs find it stressful to lair and pretend to be telling the truth. Their conscience makes the entire process stressful and makes them uneasy. Watch out for people when they look uneasy.
3. Look out for silence
Sometimes, silence is a way to lie by simply not saying anything at all. If you know someone who is usually outgoing and loud yet have become reserved suddenly, you should watch out.
4. Look out for your guts
Sometimes, the only way to know is to trust your guts. History proves that even when all evidence is against our claims, our intuition turns out to be right most of the time.