[alcover]

  ATMs might already be recording serial numbers

I've been wondering about this forever.

Say John gets bills from the ATM then pays dealer Dylan for weed. Dylan then buys a beer at a bar.

If Dylan gets convicted, and banks collaborate with the police, then John gets subjected to - at least - parallel reconstruction.

[o-__-o]

Plausible deniability wrecks that entire thesis (someone existing between John and Dylan such as a gas station)

[alcover]

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.

[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.