People who are conscious they are lying have non-verbal cues, but the tone of their voice also climbs or drops slightly, like a quarter tone. It's never easy to discover you've been cheated on this way.

There are so many tells with lies that they can be easy to spot once you know enough of them. Not all tells are absolute across everyone but if you know enough of the tells you can see them easily when several present themselves all at the same time.