When I was young and hadn't thought through the practical and ethical consequences of such practices I sold some currency at a significant markup. Used two points to justify the price and make the sales.
1. The rarity of the bill. It was the only one in the whole world with that serial number.
2. I later came up with one that had a minor amount of justification and justified an even larger markup. Two bills, each as rare as the ones in item one, but even more incredibly, with sequential serial numbers! Never mind that just about anyone can go to a bank and get a wrapper of newly minted bills with a large number of sequential numbers.
The hucksters who invented the phrase "A sucker is born every minute." knew what they were talking about.