There is a lot of information on the web that may or may not be accurate relating to distinguishing between truthful information and deception. I came across this video on detecting deception today which covers a lot of common beliefs about when someone is lying. Detecting deception is not easy, and studies have shown that most people are roughly accurate between 45%-55% of the time. In essence, their "lie detector" may as well be a coin-toss!
The problem is that people can take a 10 minute video like this covering an incredibly complex subject matter, and then apply the information within their interpersonal relationships and cause more problems than they solve...and be wrong about 50% of the time! The other problem is that most people believe they are naturally good at detecting lies. I conducted an informal survey a while back and the majority of people rate themselves at or above 80% accurate when identifying if someone is lying, so their confidence is high but their accuracy is likely much lower.
The most important thing is to get the right training and information that is supported through academic research as well as having been applied successfully in the field within real-life interviews and interrogations.