Who would you go to if you believe a judge was being unfair (or "bought off") in a court case?

A lawyer and then an appeals court.

First you have to have "standing", i.e. the right to sue. If this happened to a third party, you probably don't have standing.

Your next step is to appeal and you need to be timely, i.e. do it right away. An appeal is when you ask a higher court to reexamine a fundamental fact of the case. Obviously the appeal happens in a different court, so whoever owns this judge will need to go buy another judge. That's not real likely. In fact the appeals court might be in a different county.

If I was directly involved in the case, I would consult my attorney to determine what remedies are available.

If I was not directly involved in the case, it is likely that I do not have all the information necessary to support such a claim.