I did a wee stint as a delivery guy from Domino's years ago. I had a very young manager who had found her way into the position sort of by default when the previous manager left. She was ambitious. Domino's had a pretty rigorous accounting system - wage hours, ingredients used/wasted, number of late fees (I think it was $3 off >half hour delivery) - and the mangers were scored using it. Presumably doing well was the way to move up in the company. And, well, my manager totally cheated. Not sure how she covered all of it, but she'd usually eat the late fees herself and not record them as late, and then sympathize on the phone with distraught managers at other branches who weren't doing as well.
Point is, give people an incentive to cheat (big benefit of success, big cost of failure, low likelihood of getting caught), and many people will.