As you are looking for cheap souvenirs to bring back from Cuba, you encounter a local who is “willing” to sell you a rare item: a 3 Peso Cuban banknote with Che Guevera on it. “This was printed in very limited amounts, just under a hundred, as an anniversary banknote”.
Several tourists buy it for $10, while in fact the bill is widely available.
How to avoid: don’t do it, unless you don’t mind paying.