Actually I have a real life experience similar to the Mustang story. It was back in the 1960s when I was at Uni, I had a weekend job as the driveway manager of a very busy service station. No self service here. Drive way attendants filling your car, checking your oil and tyres and fuel was around 9 cents per litre.
Driveway attendants were not always the most qualified and were usually 14-15 year old school kids picking up some extra pocket money.
I worked the rosters and the cash register. Customers stayed in their cars and the attendants provde the service, brought the cash to the register, and then took the change back out to the customer, still comfortably seated in their car.
On one occasion an attendant came in and said $3 for petrol and from memory, 12 pints ( around 7 litres) of oil. The attendant and the owner between them had checked the oil by looking in the filler cap and then adding oil until they could dip their finger in it. After all, the customer had said "Could you check my oil and fill it up please".
Luckily for us and the owner, I was awake on the day and we pushed the car onto the hoist in the workshop (most service stations had workshops and not convenience stores back then) and the oil was dropped out and refilled to the correct level,the customer charged for one pint of oil and sent happily on their way.