Not an unrealistic senario at all. I've seen the exact thing he was talking about happen many times while working retail loss prevention.
Accidental way I've seen it is two "identicle" products that came from different factories or different distributing centers will have a slightly different UPC number. Usually just one digit difference. Both UPC have to be entered into the database seperately though. One gets keyed in at $99.99 and the other at $9.99. Now at the register level they have different prices.
Dishonest shoplifter way is that on some items, clothes and jewelry mostly, the UPC is not actually printed on the package but instead is a sticker or tag. Shoplifters will remove the UPC sticker from a cheaper product and put it on the more expensive product. Unless the register operator is paying attention or the customer goes to self checkout it gets missed.
RFID's inside the packaging might fix that problem, but currently there are no stores in my area that use RFID.
I shall politely agree to disagree then.......
My primary point here is that these folks had to use Bank /Debit credit cards.....not Oklahoma Credit Cards !
Stay safe !