I had a Saturday job at Halfords in the early sixties. There was some exciting new car stuff like flashing indicator kits to save sticking your arm out of the window and wing mirrors because most new cars didn't come with them fitted. Also Castrol oil, seat covers, touch up paint, ammeters, batteries, spark plugs, driving gloves. I don't remember any filters or drive belts. It seems very similar to what they do now and not much training was required to sell most products.
Paul