Regardless, this seems very easy to test. Just fill up a gas can and check that you're paying the right amount for the amount of gas in the can.
True the receipt protects against 2) more than 1) because the car's tank does not have an accurate guage.
I remember listening to a story once about a fraud at the gas tank in which the normal amount of gas was only given out when requested in an even increment a five gallons which was how much The Regulators requested when they came and tested a gas stations pumps. they were caught after a spicious regulator requested an odd amount of gasoline and got the wrong amount.
with a combination of receipts and camera/ML classification that classifies when a customer is filling a tank versus filling their car will allow avoidance of weights and measures regulators. This is a problem I foresee.
The places where this fraud is most likely to exist are niche markets and places where it's hard to verify. Walled gardens of software or hardware with few outputs to measure.
But they could collude... o_0
See link for a scam using an altered microchip and scheme to protect itself from discovery by weights and measures.
That said, you do specify the amount of gas if you're paying cash here in the US. You go inside, say "here's $20", and the pump will dispense exactly that.
It's worth noting that it wasn't that way the entire time I was growing up. You would pump first then pay the cashier. It wasn't until around 2005ish that I noticed signs instructing cash customers to prepay.
They can't easily cheat on prices as usually there are large signs displaying the current price. They can't easily be cheating on amount dispensed, as the pumps are regularly checked by the local Weights and Measures Department (doesn't rule out a VW like cheat though).
https://www.youtube.com/watch?v=m9HG_3SIsEM
So, your gas pump has to be accurate for the first five gallons, but then you can cheat as much as you want.
The only saving grace is that the people who make the pumps and software wouldn't be the main benefiters from cheating at the pump. So probably we're actually okay for gas pumps. It's situations where the software creator also benefits from the sales using that software...
But maybe I'm wrong. Maybe independent gas station operators are buying bootleg software ROMs to flash their pumps... "Boost revenue by 10% with this one easy trick"
And, I see from another comment:
However, in the pumps he's talking about, the machine prompts you beforehand: "Click here for a receipt". The receipt decision (yes or no) is always before. There is no way to ask for a receipt afterwards.
He always asks for a receipt (even if he doesn't need the receipt) because he figures that the machine is less likely to cheat him in that case.
More and more I see gas pumps ask if you want a receipt BEFORE the gas is dispensed. This seems risky.
If you decline the receipt and then dispense gas, the pump could cheat on the amount of gas dispensed with less risk, as a papered record of the purchase amount and price is not produced.
If on the other hand, the pump waits to ask if you desire a receipt until after the gasoline is dispensed, the dispenser will not know if a written record will be requested, and cheating the customer is riskier.
Therefore, I always request a receipt if asked prior to dispensing my gasoline.