It would be even better had one received the money in question as change from such a machine...

I was standing in front of two vending machines the other day: one for food, one for drink, and all I had was a $5 bill. I wanted food, but the food machine would only take $1s and coins. On the other hand, the drink machine took $5s.

So I put my money in the drink machine and hit the coin return. Nothing happened. I tried a few times and figured the coin return was broken or that it was out of coins. The only thing in the machine was soda, which I can't drink if I don't want to trigger my acid reflux. But I bought one anyway since otherwise my money was "wasted", thinking I'd give the soda to a friend later.

Of course, once I bought the soda, the machine spat out all my change: 3 quarters and 2 dollar coins - now I finally had coins that I could buy food with. Naturally, the food machine didn't accept dollar coins. Most machines here don't, so no food for me.

The food machine accepted coins and $1 bills, but not $1 coins or other bills? It almost sounds intentionally designed to be as difficult to use as possible. (I realize the $1 coin is larger and newer, and accepting larger denomination bills would mean dispensing more change, but still.)

USPS vending machines are well-known as the main non-bank source of $1 coins. (E.g. insert a $10 bill for $7 worth of stamps, and get 3x $1 coins back.) IIRC, a long time ago they didn't actually take these coins as payment in the first place...

I want with a guy who had fake money come out an ATM in the middle of Cusco, Peru. I offered to buy it off him as a souvenir, and offered about half face value. I was out bid by 2 others and in the end he decided to keep it as a souvenir.

That was pretty common in Peru when I visited. Or shop keepers giving it back as change.