I probably do about the same number of exams as the OP. The CAA examiner fee element works out at around £2.50 per paper set. I encourage my students to do exams in pairs (to meet the 'sittings' requirement). I also charge what I would otherwise be paid if I was flying instead of invigilating. As far as I'm concerned, this is a service I offer students, not a means of earning a living.
I keep the papers and completed scripts in a filing cabinet with a lock on it. I invigilate, mark and de-brief candidates myself. I know others who do the same. Hopefully, when we Declare later this year, this sort of thing will be inspected by the CAA during their visit. Funnily enough, I would suggest it's not the small outfits like ours that bend the rules, it's the bigger commercial concerns. 'Club admin staff'? I can only dream of having such!
TOO