Why do Jews who go to Beis Din to resolve a financial disagreement, often use "lawyers" (to'ein) to argue their respective sides. If the dayanim are capable shouldn't they be able to just heard the sides and make a decision based on the Torah? Also, doesn't this lead to the richer side being able to hire the better "to'ein" which makes it unfair?
You happen to have a very good point,in fact the Shulchan Aruch CM 13:3 and the Sma 12 write that the dayanim should really only hear from the person himself and not from a toein.
In this article Rav Hershel Schacter explains in detail how corrupt the toein system is and how people are making a fortune off this "profession ".
The point is that the individuals are often too nervous to actually show the facts of the case. Also, they are afraid that if the dayanim are not given all the arguments by their side, that they will not get a fair hearing. Part of this is the influence of the American court system. The dayanim are expected to be able to discount the to'ein when necessary.