When I was working minimum wage at a gas station many eons ago, we would have '2 for $x' specials where x is less than 2 times the individual price of whatever item.
People would often not want to buy 2, but I would ring up 2 in the till for the special price and charge them for the single. Then when the next person did the same, I would charge them for the other single.
So over the day, I would sell 10 energy drinks at say $4, but ring them up as 5 '2 for $6' specials. This would put the till up by $10, and then I would use that $10 to have a free meal.
Not me but when self checkouts were first a thing my friend would offer their countdown rewards card to anyone who forget there's and racked up heaps of points for free. I can't remember what the points go you except cheaper fuel.
Not really related, but I did ring up some flowers at a self checkout but instead of flowers, it rang up as a rewards card. I did tell the cashier who didn't give a shit, then went outside and used that "rewards card" to get money off my gas. I think it came out to about $1 a gallon