You might like to think you're good at spotting a lie, but most people actually aren't. Even if you strongly believe a coworker is lying, it's usually best to just pretend not to notice. If a coworker's lies are causing serious problems, though, you might be forced to confront him with what you know.
White Lies and Fibs
Some lies are relatively benign, because they are only intended to protect others from harm. For instance, if a coworker asks you how you like his haircut, you might not want to tell him that you think it looks ridiculous. Other lies are merely attempts to gain praise or attention, like an implausible story of a weekend adventure. Even when this type of lie is a little irritating, it usually isn't worth confronting the liar. Maintaining a good working relationship is more important than exposing your coworker's fibs.
A coworker's lies become a problem only when they affect your work, the safety of others or the purpose of the enterprise. For instance, if a coworker claims credit for work you actually did, your career can be negatively affected. If a coworker lies about performing required safety checks, someone could be hurt. If a coworker lies to cover up her errors on a project, the project could be delayed or compromised. If you suspect a coworker is lying about something important, try to catch him in the lie.
Catching a Liar
Checklists for catching a liar can be found from many sources. They usually list a series of clues you can watch out for to see if someone is lying to you. These clues can include behaviors such as talking too quickly, giving too many or too few details, not looking you in the eye or looking you in the eye too much, and supposed psychological cues such as facing a doorway or other symbolic escape routes. Unfortunately, these clues tend to be subjective, contradictory and in some cases dubious. According to UCLA psychology professor Edward Geiselman, most people without extensive training will actually be worse at spotting a liar by trying to follow this type of advice than by simply guessing.
What To Do
Clues can be useful in catching a liar if you don't think of them as evidence but as an indication to look more deeply into the matter. If a coworker tells you a suspicious story about what she was doing in a restricted area, don't just assume she's lying but do trust your instincts and check the facts. If you find out that something doesn't add up, you'll have the evidence to confront your coworker or to show your supervisor if necessary. Hard evidence is incontrovertible, while body language clues are not. Never accuse someone of lying without real evidence.