The Torah tells us in Mishpatim 23:8 not to take bribes, as bribes "blind the eyes of the wise and corrupt the words of the righteous" (my own translation).
Rashi tells us some interesting points, that even if you are being paid off to judge righteously it will corrupt and even if you are a great scholar and a righteous person you will be affected.
The Gemarah is replate with stories about Judges and Rabbis who refused to judge cases that came before them from people they had received favors from, even the most inane and indirect, for fear of not being able to judge objectively.
Nowadays people feel they are better and more moral and more objective and they can apply their objectivity despite having received small or large favors from people. Just look at all the investigations going in in our political scene. The Torah tells us that that is not the way ti works. no matter how objective you think you are, the moment you take a penny, even indirectly, your judgement is clouded.