How does this work, a gas/petrol station, for the dumb masses, having no attendant/supervisor on duty? I can imagine a private pumping station for, say, a fleet of busses, or a shipping company. There, every user would be trained and competent. I do not travel, so I never saw a non-staffed self-service petrol station, and I did not know that such exists.
I worked as a convenience store retail associate / gas station attendant. This store/station had underground fuel tanks. Fuel pumps maintained pressure to dispensers, plumbing lines between tanks and dispensers was constantly pressurised. Its dispensers controlled how much fuel would get dispensed.
What do I mean by that? Imagine a water dispenser (an office "water cooler") which has an inverted 5-gallon bottle as its supply, or imagine a beverage dispenser on a table. When you want to fill a cup of water or maybe lemonade or iced tea, you open its spigot's valve, and gravity provides pressure to dispense fluid. There could be any number of spigots, relying on one source of pressure: gravity. The gas station where I worked was not like straws in a drinking glass, where each straw sucks fluid on demand.
Once, a driver knocked/tilted a dispenser. (Ey paid more attention to eir pokeyphone than to driving eir auto.) Plumbing in its base failed, a leak formed in a joint. Gasoline sprayed inside of dispenser, flowed down its case and out onto pavement. A puddle of gasoline quickly spreaded until it reached a sewer (meant for rainwater, not petrol). I should have stopped it sooner, before it flowed over into a sewer. There was a line of customers indoors, and I did not often enough look through the window to scan outside.
Thought of a petrol station sans attendant, which any drunk or pothead or witless teenager can access, scares me.
I don't know if people running off without paying is a problem. I don't see how it could be. I'm not aware of any gas station which will allow you to pump gas without prepaying at the pump or in the store. I don't see why you wouldn't do that there. No cash, no gas. Well no ATM pin or Credit Card authorization, no gas.
Mostly for taxis, an attendant would allow post-pay. But some taxi drivers will
pay with plastic, so an attendant should not "turn on the pump"/authorise post-pay for every taxicab. So an attendant could memorise licence plate numbers, or wait until driver steps out of cab. The nice, understanding, drivers will face attendant and wave, wait for acknowledgement wave from attendant. Some drivers take post-pay for granted, as if it is
a right which comes with their job, to fuel first and pay afterward. Sometimes there is race condition: driver, tired of waiting for post-pay fuelling, breaks out their wallet to pay with plastic, at same moment as attendant grants post-pay fuelling, resulting in a
gas drive-off.
I can go on, and about more than taxis. Post-pay is a worrisome idea to sales associates, though it can make some customers loyal. I guess it is a regional norm.
Really, for how slim margins are on gas. I'm surprised they do this. Here if you want to pay inside. You have to go inside give them cash or do a credit/debit card authorization and tell them your pump number. Then you go out and fill up and come back in for change. If you give them cash the pump will stop once you hit whatever amount you hand them.
Sometimes it over dispenses by one cent, then cash register/POS computer makes a little alarm sound and pops-up a modal prompt!

That alert box has no choice of action, just "ok" or "dismiss" or so on. It is annoying and interrupts cashier/sales associate from task at hand, as it blocks view of "change due" and whatever else was on-screen.
The worst though are manned gas stations where they close down for the night. So I'm low on gas, and there's a gas station, and there's a credit card reader right on the pump, but everything is shut off and so I'm screwed.
They annoy me, those dispensers which stay on all night, with glowing screens and flashing card slots. They send a mixed message, when their dispensers and great tall sign pole are glowing but business is closed.
Only gripe I have with pre pay stations in the UK is the block they put on the card at £99 until the nozzle is replaced and receipt produced.
Where I worked, "pay at the pump" transactions were limited to $100. One who never worked retail might not believe, how ignorant and stupid can some card users be. I have many anecdotes about this. I think your gripe is dumb or misguided.
They also sell 89, 90, 91, 92, 93 octane levels- very specific.
Here's a factoid which some of you did not know: gas stations do not have as many storage tanks, as many grades of gas which they sell. Most stations sell three grades ("low mid and high" or "regular special and super" or similar) but tanker trucks only deliver two varieties, low and high "octane" ratings. Anything in between low and high, is just coming from both storage tanks, a mixture.