I think it was in the early/mid aughts when grocery stores wised up. Couponing was a big deal during that time frame and I worked in a grocery store in the States at that time that would periodically do "double" and "triple" coupon weekends. We would have people walking out with $200-300 worth of merchandise on the triple weekends and they would have to scan a candy bar at the check out so that we didn't owe them money. It was always a cart full of pretty bizarre stuff that didn't look like a typical grocery trip in strangely large amounts (stuff like 4 bottles of Windex). They eventually stopped doing the double and triple coupon weekends once they figured out how much money they were losing.

That was also before you could easily just walk into a store then turn around and sell what you bought online two hours later too.