How can you tell?
Sometime you will not now... that is true but they most likley would not be able to stare into your eyes and tell you the truth...
MOst likely they will be looking all over and they can't stop moving around..
Some people are very good liars because they somehow make themselves believe the lies they're telling. I don't think there's any way for you to know, really... until you get to know him extremely well.
Usually there is a gut feeling - sometimes you never know though.
when I lie my eyes get big!!