The Big X

There is a game show that asks people questions and then shows whether or not they have the right answer. If they are right, a large green check mark appears on the screen. If they are wrong, a large red X appears. I wish I had the ability to flash a large red X when someone is not telling the truth. If I ask a question and you give the wrong answer there would be a buzzer and a neon red X. That way you would know that I am aware of your wrong answer. When people lie are they fooling us or themselves?