Every beis din, etc.: see in the responsa of Maharam of Lublin, siman 138, regarding migdar milsa.

That the people are unrestrained, etc.: and even a single individual who is unrestrained, they can punish that individual according to what the eyes of the judge see (and so it implies explicitly in the Tur and the rest of the poskim and in the Talmud), and so wrote the Sma.

And even where there is no complete testimony in the matter, etc.: even without warning. Responsum of the Ramban, siman 279, cited in the Sma. And for capital cases they must be cautioned to act with the agreement of the elders of the city, so that they act after great need and with deliberation. Beis Yosef in the name of the Rashba, of blessed memory; and so wrote the Sma.

And specifically the great one of the generation: see the Bach, and in the Yam Shel Shlomo, chapter 9 of Bava Kamma, siman 7.

But they are not permitted to change, etc.: see in the responsum of R. Moshe Alshich, siman 59, at length.

In any case they follow the custom, etc.: see further siman 331, se'if 1, in the gloss, [as to] what is called a custom; and see the Bach, what he wrote further on this.