What capacity does any individual Jew have to decide what is or is not in accord with tradition? What is or is not authentic? Rabbis have their opinions. Sometimes they even contradict each other. But only the duly constituted Sanhedrin decides for good. And until it does, the field is open.
Well . . . how about that. Instead of needing a Sanhedrion to officially declare who Mashiach is, now we need one to declare who he isn't!
LOL...well either way, it's the same authority, no? :)