I have a well off friend who, last summer, paid to get every one of her DS's History A level papers re-marked, taken at a ££ private school, as he got a B and needed an A to do History at uni.
It cost her several hundred £, but most of his cohort's parents did the same, and most got higher marks, (a few got lower marks!) but several crossed a grade boundary, as did her DS.
It's a huge shame that poorer parents can't do that, but that's how the world works, I guess.