Gas station isn't someone. It's an endpoint, as the bar in my story. If the gas station cashier takes from the register to get a bier, you're right. If not, my thesis still holds I think.
What if I pay with 100 Euro bank note and get back "tainted" 50 Euro note and then pay in bar? Bank notes are not just collected and sent back to bank.
Doesn’t matter, plausible deniability means a reasonable person might spend it. Without knowing who’s next, you may have circumstantial evidence but that’s not enough to hold up in court.