Five Signs for Detecting a Liar

Being a human lie detector is not a difficult thing. You simply need to understand the tale-tell signs and tactics that are inherent of every liar. Here are five basic signs that are common to most liars:

1. They relax and become happier when you change the subject
A matter regarding which a person has good cause to feel guilty will cause them to be tense and have anxious. If you think that they are being deceptive while talking about a certain subject, then you should switch topics to something different and watch how they react to the change.
If they suddenly appear to be more happy and relaxed, then this can be a sign that they were trying to be deceptive before you switched the topics.

2. They stall for more time
People who are sure of themselves or honest will usually have an honest answer for an honest question and it will come to them with little thinking involved.
Not true with the liar. When a liar is caught off guard, they require time to formulate a response that sounds legitimate. Therefore, they might employ a stall tactic to buy more time.
One commonly used way a liar buys more time is by employing rhetorical questions such as: "Can you repeat the question?", "What do you think?", "Could you be more specific?"-or they repeat the same question back to you.
Recognize these kinds of questions as delay tactics, used to buy more time to create a believable lie.

3. They use absolutes
Absolutes should be a red flag to you when a person is trying to be deceptive, because absolutes are most often lies in and of themselves.
Absolutes are words like, "always," "never", "everytime", "everyone". Listen carefully for absolutes because they are used in two main functions: when the person is trying to persuade you to do something, or when they are getting defensive about something they did.
It’s a known fact of life that there are no absolutes. Even the cleanest person has gotten their hands dirty at one point. No one is perfect and we learn from our mistakes
That is why absolutes are often associated with deceptive behavior - because they are untrue to begin with.

4. They don't defend their honor
When a person is faced with a false accusation, the normal tendency is to become outraged and react aggressively towards that accusation because it's an attack on their reputation and their honor - both of which an individual has a psychological need to defend. "How dare you say that to me!" would be a typical honest response to a false accusation.
The liar, however, will not protest the accusation, but rather be focusing more on what to tell you in an effort not to sound as guilty. They might use stall tactics such as blurting out a "NO..." and then pausing to follow it up with some type of rational explanation.

5. They use "Just kidding!"
While most of us use the phrase, "Just Kidding", as a common part of our conversation to playfully jest at another person, there is a psychological aspect to this phrase. "Just kidding" is a minimizer phrase, meaning that it downplays the harshness of what was said before it.
Even if we are innocently joking, there is at least some partial truth in what we just said, otherwise we wouldn’t have said it in the first place. We then slap on the minimizing phrase, "Just kidding" as a way to show the other person that it was "all in good fun".
It might be all in good fun, but remember that when someone says this phrase, they probably believe in what they said previously - at least a little.

source: http://www.hodu.com/liar.shtml