Most people wouldn't take it back.
I do think if it's memorably expensive you have a chance.
The stamp/coin/card guy I hang out at in college took back a bad coin something like 10 years after selling it. He did remember the fairly regular customer, AND the coin. No reciept, but they both recalled the sale as being "about $x" so that's what got refunded on the spot. The altered coin went off to the smelter.
I might ask, expecting nothing.
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