Bar Code Switching
A particularly clever form of retail theft—especially when salesclerks are working fast and don’t know the products—is to switch bar codes. This particular thief stole Lego sets. If you know Lego, you know there’s a vast price difference between the small sets and the large ones. He was caught by in-store surveillance.
EDITED TO ADD (6/12): I posted about a similar story in 2008.