I honestly do not know what is to keep a person who has been asked to judge from showing favortism. If I and other students have made an enemy with a well connected instructor who is dancing his students in our heats and he is friends with a judge and has trash talked us and our professional, what, HONESTLY, is to keep that judge from scoring us down and his little friend up? I'm sure he believes everything his buddy has told him. As for my position, it's bad form to question scores and any evidence I could possibly have of favortism would be shaky at best. I do know that, "Everybody knows they are friends" would not cut it, not one bit.
I mean, honestly. Other than ethics I don't see what would stop this. I just know that there isn't a single thing I can do about it. People are just people, I don't care what sort of hat you stick on their heads. The only answer I have is to dance my best and know that they are only hurting themselves if it is obvious the scores are unfair.