No matter what the crime, be it shoplifting, pedobaiting or even credit card fraud, Social Engineering is key. While shoplifting, one doesn't want to give off any hint that their doing something illegal but if you look sketchy you might as well be yelling, "Hey look at me, I'm stealing!" and it's all about body language. If you know how to read body language well enough, you may even be able to spot those tricky casual clothed LP.
Another example would be if you caught some pedo and got him to meet you IRL. Say you want pose as a cop and threaten to lock him up for something. Any Joe Shmoe can go and buy a police costume, but that doesnt mean the pedo is gonna fear him. Now if you can sell yourself and persuade this guy that you are indeed law enforcement, well he might do anything you want.
Now I can go on and on about how important social engineering is or I can just get to the point and i'm sure you would prefer that.
Enclosed in this RAR, there are a few ebooks that specialize in reading body language, teaching you to control your own and other on persuasion/negotiation. I do hope that you will put them to good use.http://www.mediafire.com/?dgfrti69b9j8ulb
EDIT: Fixed the Link