I worked at a place with a neat twist on this concept - the secret shopLIFTER. They'd come in and steal a bunch of shit. If we caught 'em they'd give us the stuff back and show a badge that proved who they were and why we shouldn't tie 'em up and put them in the security room (yes, we did that with the occasional real shoplifter
)
If we didn't catch them, they'd report us, we'd catch holy hell from the corporate office, AND the secret shoplifter got to keep whatever they stole.
The only trouble was that they'd keep the ID card in their wallet, which would be in a pocket, and my store was in a bad part of town where the real shoplifters liked to pull knives or guns on us. So sometimes the secret shoplifter would get a little roughed up when he reached into his pocket too fast to show his ID