I used to this (also drive a badged vehicle so no hiding!), however just after Coles took over my local, I got petrol and moved into a parking bay, and then went into the store and paid as normal. Nothing was said, nor anything untoward.
About a month later I received a "final demand" payment letter, including advice that I was now going to be prosecuted for a crime (theft by deception IIRC). As I had already paid (and checked the invoice/receipt to make certain), I contacted the number to advise I had already paid, however was told there was nothing they could do now, and to turn up in court when I received my summons.
They took me to court, where I provided a copy of the receipt, and an extract from my bank statement showing the payment, the case dismissed in a matter of minutes. Sitting in the waiting room, there were at least a dozen I recognised from the same station - all of whom probably in the same situation. What a waste of time.