How can you tell when someone is lying to you?

There is no way to really tell from body language, especially with an experienced liar.

Good Question.
I remember reading a book on this once, and it helped a lot. I could link a website, but for now I’ll just go with what I know:

Signs of Lies

Lack of eye contact—big one
Touching any part of their face/hair—this makes them feel more comfortable in the situation of a lie
Avoiding the straight out lie/question response/stretching the truth—i.e.: if you ask “did you do this?” and they say something like “why would I do that?” or “that’s stupid!”
Stuttering/choking—things like “ummm” or “uhhh” or taking a while to respond, or something like saying “nnnnnnooo” instead of just “no”.
A fake smile—you can tell this if it almost seems forced; If it looks as if there is almost a blank expression within the “smile” then it is probably not real. Try to see if their showing teeth, that’s a sign of a real smile, and so is squinting of the eyelids. Smriking is usually fake.
Swearing—this helps them express their anger of you asking a question that they don’t want to answer truthfully. “No, I didn’t eat your #*&%ing piece of cake!”

Signs that they are telling the truth

Opposites of ones above—(Eye contact, real smile, etc.)
Touching throat or chest—I don’t really see this one too often, but I remember hearing that it is one.

Keep in mind that not all of these may apply to everyone or anyone. Some like me can almost game the system in knowledge of these things and go against these rules, or some are just straight up good at lying. I almost see it as a humans’ sixth sense of being able to tell lies or at least for me it is, so go with your gut.

Mostly through personal experience, I guess. But I’m a bit naive here, though. I usually take whatever a person says at face value until I learn otherwise. If I discovered someone lied, and the lie affected me personally, that’ll be the last lie you get to tell me.

Body language and tone of voice….choice of words is a big part of it as is eye contact

According to a retired police detective of 13 years, it’s a persons eyes.

When the suspect gives an answer, watch his/her eyes. If they are not looking straight at you and answering your question, then this person, most of the time, is not telling you the truth.

@john65pennington Hmmm…I guess politicians and used car salesmen are exceptions to that rule.

The only way I am able to tell whether someone is lying is if their statements don’t add up. For instance, if someone tells you they are allergic to peanuts, but you’ve seen them eating peanut butter cookies, something else is going on—either they think YOUR peanut butter cookies are terrible or they are on a diet and don’t want others to know it.
I can usually tell if someone is holding back (as opposed to direct lies) if they don’t answer a question directly or couch their answer a little too tactfully.

@lynfromnm Now, that makes sense to me. You see it a lot in interviews. Someone answers a question with a 10,000 word thesis that has nuthin’ to do with the question being asked. And everyone listening nods knowingly like something really profound was explained. Lies, lies and nuthin’ but lies.

Eye position is a good indicator.

The primary issue with lying is that there are behavioural patterns amongst humans that indicate that they’re lying, but these differ in type and intensity just enough between people that it’s very difficult to measure. Hence the inadmissibility of lie detector tests as legal evidence. In addition to this, alot of picking up on a tells comes down to the, sometimes over-estimated, perceptions of the “non-liar” involved.

I’m unfortunately guilty of dropping a lie in conversation from time-to-time, and when doing so I try to make a point of giving direct, plausible answers, maintaining eye contact and generally not acting abnormally specifically because I know people presume those to be major universal indicators; I have no doubt that others who are lying also take this into account and act accordingly.

Overall I’d say the best manners with which to determine whether a person’s lying are firstly through basic logic as mentioned by Saboteur previously. That is, if a person’s statements simply don’t reflect reality they’re either lieing or misguided.

Secondly, through experiencing a person both when they’re being honest and when they’re lying on a reasonably regular basis. The longer and more intimately you know an individual the more likely you are to discover a lie quickly. This is especially interesting to observe in strategic games or sports such as poker or boxing wherein the period of time set to establish an understanding of your opponents behavioural patterns is limited but can be very rewarding if done well.

I know a lot of people are saying a person who doesn’t meet your eyes is lying, but in some cultures that’s just polite. I know a lot of Native Americans who feel that look right at someone is a challenge, and is disrespectful. Maybe the same is true in some other cultures as well.

All I’m saying is, don’t let JUST the element of not meeting your eyes make you sure someone is lying.

Eye position doesn’t mean looking into your eyes. The direction of someones eyes is an indicator of what part of the brain is being used, and one certain direction indicates the part associated with inventiveness and lying.

Be a detective… Ask questions. Have them explain the details of the story. Come back later with some ruse to discuss it again. Look for flaws and inconsistencies.

The problem with lying is that you end up having to lie more and more to cover the original lie. Therefore, as the liar embellishes the details, there are more opportunities for you to trip them up.

They aren’t specific when it comes to details. Since it’s a lie, it will be dificult to elaborate on something that never happened. Ask for a few details and watch the response.