But that is the problem - there is a perception the suppliers are trying it on. No industry providing a mainly discretionary service can survive if they rip people off. The result is that industry contracts, there is less revenue and so the rip offs increase.
If these people had any sense they would put a credit card machine on the pump the same as most garages and then there would be no excuse for these additional charges. They might find they sell more fuel.
Of course, it isnt universal. A few months ago, night training at Denham, we were mulling over a final flight that might have taken us beyond closing time when, without prompting, we were told there would be no charge if it was only 15 minutes or so. That attitude may contribute to the fact that Denham is often busy when other fields are dead......