I actually did some extensive google research once on how to tell if a guys lying to you haha. One tip that I really found to work is to watch what direction their eyes go. This has just about always worked for me except in situations that you can't see their eyes, like when talking on the phone or computer blahblah.
Anyways, if a person looks to THEIR left, it usually means they're lying. There's a part on the left side of your brain that is the imagination side of your brain. So when they look to their left, it usually shows they are thinking of something to make up. Something to imagine. Therefore this usually shows that they are not telling the truth.
If their eyes go to the right, it usually means they're telling the truth. The right part of your brain is your memory side of your brain. So if they are look to the right, it usually means that they are trying to recall or remember something which shows that they're trying to be honest about what they have to say.
There were also little tips like if the person avoids looking at you, fidgets, or touch their nose when telling you something they are probably lying.
Like I said, the eye one I've actually used on people before. I don't tell them this because then they can pick up on it and try to not let their eyes go in certain directions, but it really has truly worked multiple times for me. So I hope that helps at least a little.