I worked at a Sinclair in Cleveland in the 60s as a teen.
We really did do full service back then.
Most everybody paid with cash. I think we took credit cards but it was very uncommon.
I remember my dad rolling down the window, handing out a bill and saying 'Give me a buck's worth of regular'. Now- if you can even find a station that'll pump it for you- they'd just smirk and come back with a shot glass full of gasoline.