[miskin]

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.

[alcover]

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

[o-__-o]

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.

You don’t punish someone based on chance.