Keygrip, sorry but here are some details I didn't mention earlier...
Closing the storm window wasn't on any checklist. It would be completely reasonable to charge people if they had been told they had to close the storm window and there would have been no arguments at all, had this been the case.
Yes, a pen. Two people were charged for leaving a plotter in the same aircraft and neither of them had left it there. They decided not to move it so if the student who had dropped it came back, they would have no problems finding it. One person was charged for leaving a cushion in the aircraft, a cushion that someone else had left on the seat previously. Of course some people did leave actual rubbish in aircraft like coffee cups etc and other things you referred to and those people were fined justly as that WAS stated as a ''no-no''.
If only they did clean the aircraft
, they would be decent if they were given a wash every now and again...
As I said, we would have paid any fines and taken full responsibility for not following the rules if we had known that they were the rules.