A man buys a pack of cigarettes with a $50 bill. As I count his change back to him, he asks what he’d paid with, and I tell him it was a $50. He asks to buy it back, and counts out $49 in smaller bills and lays out 99 cents on the counter. I hand him the $50 for the $49 while he fishes for the last coin he needs. He comes up with a $1, which he gives me, along with the $50 and asks for a $100 instead.
We don’t have any $100s, nor other $50s. While I’m trying to figure out how to give him his money back, the fact that this is a scam occurs to me. I tell him, politely, that $50 of the money in my hands is mine, and he can either have the $50 bill or the small bills. He chooses the small bills. He then asks if he can buy the $50 back, and I let him.
Surprise, surprise, he tries the scam again, but this time I’m watching to see how it works, what he’s doing, and what I need to watch for in the future. Once he hands me the $50 back to ask for $100 again, I tell him he’s scamming me and is no longer welcome in the store. He grumbles a bit as he gathers up the change, but goes.
The next morning I come up $50 long. Apparently when I was kicking him out I forgot to give him his $50 back. So, to recap, I learned how to spot this kind of thing AND he ended up losing $50 on the deal. And if he hadn’t been greedy, and done the same kind of thing using a $10 to get $20, I wouldn’t have had the momentary confusion and he might have gotten away with it.