I worked in a grocery store for a number of years.  The vast majority of overcharging had to do with products having to be marked with a sale price while it was on sale and then having to remove the old labels replaced with non-sale price labels after the sale ended.  I'd say that 75% of all pricing errors occurred because of this--no fraud involved.

Ninety percent of the remainder of the problem had to do with minimum wage teenagers not peeling off old labels and putting on updated ones (as they were supposed to do) when the store absorbed a price increase.  Again...no fraud--just punk kids getting some work experience and sometimes screwing up.  (Did you know that even I was once a punk kid?)

This misguided law is based on a deep-seated distrust of job providers.  It is a seemingly benevolent action taken by anal retentive government regulators to keep defenseless consumers from being ripped off. The result of which has been, of course, the hiring of a few more regulators, higher prices at the store, and consumers being ripped off. Shocking, I know.