Albeit KnowLaw is coming off a bit snarky in the delivery, I was thinking of a retort.

David, defacing currency won't be a matter determined by the Fed bank/shopkeeper, it'll be decided in a court.

That court trial could start with the shopkeeper. The shopkeeper could easily become the prosecution's prime witness to convince a jury that you indeed defaced the currency to a point where it is unacceptable.