It’s a common misconception that the telltale sign of a liar is being shifty-eyed, i.e., avoiding eye contact. But this is not necessarily the case. Avoiding eye contact could be a sign of being untruthful, but it could also indicate nervousness or some other emotion. Furthermore, because it’s common belief that averting eye contact is a sign of untruthfulness, a pathological liar may be certain to maintain eye contact to appear more truthful. A more reliable sign of deception is voice pitch, which tends to rise when a person is lying, though even this may not be present in a sociopath.

See also:
Psychology Today: “Spotting the Liar”
Harvard Business School: “The Truth Behind the Smile and Other Myths – When Body Language Lies”