In my profession, I am lied to on a regular basis. Since I have been a professor for quite some time, I have learned a fair amount about the ways of lying. It also helps that I teach critical thinking and include a section on assessing credibility.
Interestingly enough, many people think that they can discern whether or not a person is lying by examining their behavior. This is presumably based on the assumption that there are behavioral clues to indicate when a person is lying. These include the usual signs of nervousness or anxiety such as a failure to make eye contact, sweaty palms, seeming tense, and so on. Unfortunately for those who need to discern lies from truth, such behavior is not actually an indicator of lying. People lie without showing any signs of nervousness and people show these signs when they are not lying.
One argument for this can be based on the obvious fact that there are plenty of successful liars. As has been said, a successful con artist will seem quite honest-after all, if he seemed dishonest he would not be successful. As such, it is quite reasonable to believe that there are people who lie without showing the signs that a liar is alleged to show.
Naturally, it might be countered that some people are skilled at lying and show no signs of their deceit or that others are merely bad at detecting said behavior (or both). This is, of course, worth considering.
My own experience has been that people are generally good at lying without showing any physical signs they are lying. Over the years, I have lost count of the number of times students have lied to me with perfectly calm voices, solid eye contact and no sign of discomfort. The only reason I knew they were lying was because I had clear evidence of this. One of my most amazing experiences was when a student came to my office to say that I had lost her test. I showed her that I had counted the tests, had everyone sign in, and also collected an assignment. All tests were accounted for, she had not signed in and I had no assignment for her. She left, then came back to say that she missed the test because she was sick. Her behavior was completely normal-no change of tone, no nervous behavior and so on. I said that she would need to bring an excuse from the Dean. She left, then came back a bit later to tell me that she had been in a car accident, which is why she missed the test. I again said she would need an excuse from the Dean. Now, it might be claimed that I was oblivious to incredibly subtle behavioral clues that she was lying that someone else might have caught. However, she showed no discernible anxiety-she merely conveyed an air of boredom and disdain. It seemed like the whole thing was routine to her and she was apparently put out by my failure to simply go along with her.
After a spike in students trying to change answers or names on returned tests, I started taking photos of all the answer sheets with my iPod touch. When a student would come in with an exam claiming that I had made a mistake, failed to record a test grade or that I had lost a test, I’ll whip out my iPod and look through the photos. Interestingly, the students never showed any signs of being nervous-even when the photos exposed a lie. It seemed like lying was but a tactic that had failed and they took it in stride with no change in behavior.
It might be countered that I was dealing with a few master liars or that I am simply incapable of basic observations regarding anxiety. In regards to the first, it is certainly possible that I have encountered many master liars over the years. After all, I have about 300 students a year and have been teaching for a couple decades, so I could certainly be encountering people who are unusually skilled at lies. It is also possible that although I am capable of observing behavior, I simply cannot discern anxiety caused by lies or other lying behavior, although I can detect other anxiety just fine (such as that shown by students who are worried about failing).
I do not want to convey the impression that my students are unusually prone to lying. Based on my experience with other people, they seem to be quite normal and most of my students do not lie to me (if only because there is no need to do so).
Interestingly enough, I do see what would be regarded as behavioral indicators of lying from people who I know are not lying. After all, signs of anxiety or stress can result from many causes that have nothing at all to do with lying. Also, some people just normally exhibit behavior that is wrongly taken as signs of lying, such as being unwilling to make eye contact, nervous laughter, and seeming tense.
Not surprising, the only really reliable way to tell when people are lying is to have actual evidence indicating they are saying untrue things. This is not to say that people never show physical signs they are lying-sometimes people do show nervousness or guilt when lying. But, trying to go by the alleged behavioral clues is a recipe for getting things wrong.