In our case, pilots who uplifted fuel away from base (except where we had an agreement) would only pay the difference between our price and the other price. So uplifting 40 litres, in those days, would have cost him about £4 as he would have been credited the balance from his rental bill.
As for leaning, a private owner with decent CHT, fuel flow and EGT indications should be able to find the best mixture setting. But most of the rental wreckage around at clubs isn't so equipped and excessive leaning (I flew with one pilot who (briefly!) pulled the mixture back to the point of rough running at 1500 ft), can damage engines. We had to change a pot once at the 600 hr point - someone had cooked it through excessive leaning......
With all the advances we've seen in electronics, it surprises me that most of the GA club fleets still rely on ancient carburetted engines with manual mixture controls and the ridiculous need for carburettor heat. Even the cheapest car with a much more complicated engine usually has electronic fuel injection and a reliable EMU these days - but many light aircraft are stuck with some carburettor from a 1950's combine harvester!