Question

What most often gives away liars? inconsistencies in the things they say nonverbal behaviors personal confessions none of these; liars are very hard to detect?

Answer 1

I believe the answer is: nonverbal behaviors 

For example, stutter and inability to maintain eye contact could be considered as a sign that the person lying.
On top of that, liars often shows signs of physical discomfort while doing it such as causing them to touch the back of the neck or constantly scratching their heads.