The judges do not know who is a member and who paid the non-member fee for that show....
I know biases (and more likely poor judging) can happen, but I think people would be surprised if they ever saw a copy of the judge's cards.
I attended a judge's clinic once where during a mock flat class the judge pulled one of the riders aside and asked him to "accidently" drop a stirrup in one corner of the ring by the judge and very discreetly pick it back up. Having the best eq in the class everyone participating in the clinic was shocked that he didn't win it. The judge asked if anyone else noticed that the kid had dropped a stirrup. Because of where he was on the rail no one saw it. You don't REALLY know what the judge was thinking/saw unless you talk with them or read their cards.
Also, I know a judge who was judging a particularly bad class where the kid had some major fault. The judge was CRINGING to have the rider win the class but was unfortunately the best out of the group. The kid went around thinking that fault was completely ok when in reality it was just a tad better then the other major faults the rest of the group had.
IMO, regardless of level of the show you ride as if riding at the top. Follow the rules and find out what the judges want!