Cyd,
First, life isn't fair. I'm not saying that people shouldn't strive to improve situations that might not be fair, but in the end true fairness likely won't be achieved.
Second, and more to the topic at hand - judges are not given a set criteria upon which to judge ballroom dancers. I've never seen any set criteria that says they must base 25% of a mark on footwork and 35% on frame and 15% on floorcraft, etc. So maybe that's a place to start. If judges have a set criteria it's somewhat more objective to see if the judges are actually basing marks on that.
Third, I've seen a particular judge who has a personal grudge against a certain couple. The judge NEVER marks them into a final, and the judge ALWAYS marks them last when the couple makes the final. Despite that judge's marks, the couple has still won events when that judge is on a panel. So, ONE judge's marks shouldn't make or break a result. That's one reason why there are several judges on a panel.
Fourth, I don't believe that EVERY judge who has a student in an event is automatically a corrupt judge. And, even if there is a corrupt judge it may not have to do with money/lessons - it may be something else that's affecting the marking of that judge. So tracking judges based on money might be a red herring.
I saw an event where a wife was on the judging panel when her husband was dancing in the event - and her marks put him in the bottom of the pack, which is where he wound up in the end. Should she have been on the panel? Of course not; but there it was. And seemingly, she didn't give him favorable treatment. Also, there were two other judges on the panel who I know had given coaching lessons to every single couple in the final. This was a small competition and if the organizer knocked three judges off of the panel, there weren't other judges on hand to fill in. If there were dancers who didn't like it, they didn't make a formal objection. Maybe next year they will quietly not attend that particular competition anymore.
So - in the grand scheme of things, maybe there's a judge who is marking a couple poorly or well for one reason, but then another judge marks a different couple poorly or well for other reasons. It probably all "comes out in the wash" in the long run.
There are unfair umpire calls in baseball and unfair referee calls in basketball - by supposedly impartial umpires and referees who don't coach the players. Why do they make unfair calls?
Are there unfair marks in ballroom dancing too? Sure. And if I see someone breaking a rule and if I can show chapter and verse of the criteria being broken, yeah, I'll raise an objection. But it's easy for a judge to justify a subjective mark when there are no set criteria.
So, after all of my rambling reply, in the overall scheme of things, there are other battles that I'm more willing to give my attention too.