Perhaps more of a theoretical shailo then a practical one. If a Dayan would be dealing with a case between Reuvan and Shimon would it be a problem of accepting shochad from both of them if they were giving the same amount of money (let’s each $500.) Is there anyone that speaks about this point?
This question is not theoretical, and it is a very practical matter.
It is forbidden to accept bribes even if both are giving the same amount, as we find in Kesubos 105b.
The Penei Yehoshua understands that this is because it can lead to actual shochad, whereas the Sema (9:2) explains that the Torah forbids all types of bribes, because the decisions of the judges cannot be influenced by anything other than considerations of halachah and truth, and there is chance that the money will somehow be part of the decision.
See also Meiri, and Birchei Yosef 9 (who notes that the bribe can cause the dayan to judge both parties for the good, and this is also a problem).