Dishonest mediators and arbitrators

Hello everybody,
A question: what prevents mediators and arbitrators from dealing with one of the two sides in exchange for a part of the “booty”?
Or even, what prevents a mediators or an arbitrators from giving reason to himself using another computer from which he carries out transactions?
I feel obliged to specify however, that I have completed numerous transactions with a lot of satisfaction on Bisq and that the very few times that unfortunately the other party forced me to deal with mediators and arbitrators, they behaved more than very well and honestly.