Comment by Aurornis

In the fraud/theft detection I had some experience with, everyone learns right away that mistakes happen all the time. Singular incidents are basically not worth investigating unless something about them is highly unusual, like an unusually large dollar amount or aligning with a scam that has become popular.

When I watched movies and TV shows I had this idea that thieves were all clever people who built smart systems to evade detection and steal right out from under big corporations. Some of those people might be out there operating undetected, but the average thief who gets caught is someone trying to abuse something as much as they can until they get caught. Some of them are so brazen (like the scan everything as bananas post above) that they must believe that nobody will ever check and if they do get caught nothing bad will happen.

The staff who watch these things have a good sense of what dollar thresholds the customer must cross before getting law enforcement involved.