Break it down...
Is it someone who claims to be God? Or is it someone who holds some kind of special/direct communication with God?
And who gets to define this person as a madman or a spokesman? The prophet or the spectator? Back in the day the Jews affirmed a teacher of the law as one having authority by having two "authoritative" types place their hands on him.
Which raises the question... should we be able to recognize a genuine prophet? Or should a genuine prophet be the kind of person who was always surprising people and out-boxing every box others tried to put him in?
As I see it, a genuine prophet is the kind of person who speaks of risk when we'd rather hear comfort... and comfort when we'd rather have risk... who proclaims division when we'd rather have peace... and peace when we'd rather have division.
The kind of person whom you couldn't put your finger on... that is, until you held him down and crucified him.
"He was in the world, and though the world was made through him, the world did not recognize him. He came to that which was his own, but his own did not receive him. Yet to all who received him, to those who believed in his name, he gave the right to become children of God—children born not of natural descent, nor of human decision or a husband's will, but born of God." (John 1:10-13)