I used to ask questions like that but it only gave me headaches and kept me up nights. And the people with thousands of dollars in old stamps are worse.
I suppose unlikely is a good word, but … I have had several customers spend a commemorative silver dollar, both the regular ones and the ones folks sell painted.
And once I had someone who had one of those 1/10 ounce commemorative gold coins. “This is five dollars, right?” “Says right on there, 'Five U.S. Dollars. Sure, I’ll give you five dollars for this.”
Yes, I contact the police in case anyone has reported them stolen. So far, I always get to keep them.
I used to stop at a little store once a month (as my reward for dropping off my rent check on time) where the proprietor really liked the golden dollar coins.
He played darts competitively, so he spent a lot of his free time in bars, and he’d found that just tipping generously doesn’t make you memorable, but tipping in little gold(en) coins does, so the waiter will remember you (and that you tipped well) on your next visit.
So I would buy any that came through my drawer to spend them there, and once even went to a bank to get a $25 roll just so I’d be stocked up.