For a judge not to accept a bribe
“Do not take a bribe” Shmoth 23:8, even to render a true judgement.
The bribe is to be returned.
Bribery of words (flattery) is forbidden.
Whoever give a bribe violates “do not place a stumbling block before the blind” (-76)
Since he is unable to do other work while he is occupied with the judgement, it is permissible for him to be compensated and take payment from both litigants equally.