In Stud Terkel's Working, there's a wonderful interview with Anthony Ruggiero, an industrial investigator. Here's one particularly fun portion:

What happened is this: say I'm an agent and you're an employee. I'll go over to you and I'll say, "Hey, I seen a TV over there. I wonder what the chances are of gettin' that out." You as an employee would more or less go along or say, "You're crazy." But if you're an agent too, you're gonna feed me. You're gonna say, "Yeah, how the hell could we get it out of here?" And that's what happened. (Laughs.) As soon as I gave him the bait, this other guy says, "Right. What do you think we oughta do about it?" So I called up my office and I said, "This guy, Hal ..." They said, "Forget it. He's one of our own men."

At this point, Terkel inserts an even more fun footnote:

A news item: Bangkok, Thailand (UPI)—"Police battled a gang of bandits in southern Thailand Saturday. One bandit was killed. A police spokesman said the battle began when the bandit gang, disguised as policemen, challenged a group of policemen disguised as bandits."

This is pretty reminiscent of G. K. Chesterton's The Man Who Was Thursday. I highly recommend it.