When people lie, it's common that they break eye contact, but the liar could go the extra mile to maintain eye contact in attempt to control and manipulate you.
"[Bernie] Madoff, like most con men, overcompensated and stared at people longer than usual, often without blinking at regular intervals," says Glass. "When people tell the truth, most will occasionally shift their eyes around and may even look away from time to time. Liars, on the other hand, will use a cold, steady gaze to intimidate and control."
Also watch out for rapid blinking.