I have observed that when an item, say a can of green beans, is on sale, and I buy several of them (within the limit for the sale), the last one rung up is at the regular price. This has happened several times to me for various products and I get my money back for that last item, plus the item for free.
When an item scans incorrectly I mention that it is free to the cashier...they don't all know this. I recall one cashier sneering at me and saying "I'll have to call the manager for this, I can't take YOUR WORD for it."
