Without a receipt there are two things that can be a problem: 1) Less gas is pumped, 2) Charged more than the pump said.

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.

Gas is common enough and such a hot button issue that mass fraud like that would be easily noticed on credit card statements and in the tank. It's easy to test, confirm and verify, and can be done by just about anyone. Pull up to the station, fill up your gas canister, and check the price, volume etc.

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.

On the other hand, there's a reason why the pumps have those weights and measures stickers on them.

Car manufacturers could also install more precise sensors in the gas tank and report the amount of received gas.

But they could collude... o_0