Years ago. Before the Internet one of my managers brought me a handwritten letter accompanied with a receipt for dry cleaning a leather jacket. Our Accounting Manager was about to pay it. The letter explained that the writer had been in our restaurant the prior Sunday night and one of our staff had spilled tea on his jacket.
The manager and I smelled a rat.
No buffet on Sunday night as mentioned in the letter
No mention of the incident in the shift or MOD log
Why would anybody be wearing a jacket when it was 82 degrees that night?
I brought this up to our corporate Loss Prevention team and it turns out that this same letter writer had "visited" many of our hotels and others that same night.

The guy did some time once he was tracked down.