How to Detect Lies
Watching facial expressions in order to determine whether a person is lying might just save you from being a victim of fraud, or it could help you figure out when somebody's being genuine. Jury analysts do this when assisting in jury selection. The police do this during an interrogation. Of course a polygraph does this, but it is a little heavy to carry with you. Therefore, you have to learn the little facial and body expressions that can help you distinguish a lie from the truth.
Observe how the person smiles.

Forced smiles are easy to spot since they only involve the muscles around the mouth. The person will appear as being overly relaxed and not really happy. Look at the mouth and see if the teeth are showing. A real smile will reveal a bit of teeth but a forced smile will not.

In a real smile, more facial muscles besides the mouth are involved. A dead giveaway of an honest smile is tightening around the eyes, which sometimes causes crows' feet. Very few people can fake a smile and still control their eyes in this manner.

Watch their hands, arms and legs, which tend to be limited, stiff, and self-directed when the person is lying. The hands may touch or scratch their face, nose or behind an ear, but are not likely to touch their chest or heart with an open hand. 

Check for sweating. People tend to sweat more when they lie. 

See if they are telling you too much, like "My mom is living in France, isn't it nice there? Don't you like the Eiffel tower? It's so clean there." Too many details may tip you off to their desperation to get you to believe them.
Notice the person's eye movements. Someone who is lying will be more reluctant than usual to make direct eye contact. Liars also tend to blink more often. (Proverbs 16:30) A typical right-handed person tends to look towards his left (your right) when remembering something that actually happened (remembered images, sounds and internal dialogue) and towards their right (constructed images, sounds and kinesthetic sensations) when they're making something up. 
Be sensitive to the person's emotional expression, specifically the timing and duration, which tends to be off when someone is lying. Emotions can be delayed, remain longer than usual, then stop suddenly. Likewise, they might not match appropriately with verbal statements. And, as with smiling, facial expressions of a liar will be limited to the mouth area. 
Pay close attention to the person's reaction to your questions. A liar will often feel uncomfortable and turn their head or body away or even unconsciously put an object between the two of you. Also, while an innocent person would go on the offensive, a guilty person will often go immediately on the defensive. 
Listen for a subtle delay in responses to questions. An honest answer comes quickly from memory. Lies require a quick mental review of what they have told others to avoid inconsistency and to make up new details as needed. 
Be conscious of their wording. Verbal expression can give many clues as to whether a person is lying, such as:
o	Using/repeating your own exact words when answering a question 
o	NOT using contractions 
o	Avoiding direct statements or answers 
o	Speaking excessively in an effort to convince 
o	Speaking in a monotonous tone 
o	Leaving out pronouns (he, she, it, etc.) 
o	Speaking in muddled sentences 
o	Using humor and sarcasm to avoid the subject 

Allow silence to enter the conversation. Observe how uncomfortable and restless the person becomes when there is a pause. 
Change the subject quickly. While an innocent person would be confused by the sudden shift in the conversation and may try to return to the previous subject, a liar will be relieved and welcome the change. You may see the person become more relaxed and less defensive. 

Tips 
•	Just because someone exhibits one or more of these signs does not mean they are lying. The above behaviors should be compared to a person's base (normal) behavior whenever possible. 
•	Some of the behaviors of a liar listed above also coincide with those of an extremely shy person, who might not be lying at all. 
•	Some of the behaviors may occur also when somebody is very concentrated on speech (for example when the topic is sophisticated or the person is stressed) 
•	Botox or other plastic surgery may also interfere with 'tells' and give false positives.