But even at exchanges, the bid for $50s was beating the ask for $1s, I was thinking there's a trivial arbitrage opportunity haha.
An easier option if you have one, is going to a forex office in Vietnam or somewhere - and even then they may not take it.
I was lumbered with a couple of them for a few years, until I dumped them in Uruguay.
I'd brought USD notes from Europe to spend and as an emergency fund. They were all brand new (sequential numbers) $50 notes, just what my bank gave me.
At the end of the trip, I swapped about $300 of old notes the tour staff had for $300 of new notes. This included a very slightly damaged $100 note which the tour guide said had been a tip, which he was unable to use because of the damage.
So as US currency degrades over time it slightly loses inter exchangeability in the third world.
I did have a food stand on the boardwalk in New Jersey once refuse a worn bill, which was wild. I think it was a $1 and it may have been slightly torn near a corner. I'd expect that if using USD outside the US, but I guess Jersey is different.