To catch a liar (lawbreaker, cheater, villain…etc), you need to think like a crook. Does this mean the individual good at finding liars is just as bad as a crook? Also, why would anyone think about hiring an individual supposing good at identifying liars when there is a chance the same individual could cheat the employer that employees that individual. In my opinion, the answer rest on the person making the decision for the department / firm.