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.
You're right but the higher the denomination, the smaller the chance it'll serve as change.
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.