An interesting conundrum you have before you sbf! It's the central issue when someone arrives on the scene (a Moses, a Jesus, a Muhammed a Baha'u'llah) and claims to represent the divine. Either that person is a) telling the truth regardless of how out of sinc with contemporary world view is in vogue with the masses) or b) the person is exceptionally delusional beyond the run-of-the-mill nitwit or 3) the grandest of fabricators who has exceptional knowledge none of us possess and uses it to conjure up the wildest of schemes. Your delimma then is to prove or disprove for yourself which of the three is the case.
Now, by what criteria does one do that? There are biblical standards left to us, but they are vague by most standards and perhaps run the risk of circular reasoning when one claimant defines the way to identify the legitimacy of a future spiritual giant in some "end time" then equates to this person's own "return". A complicated and amazing milue to wade through and remain in some semblance "objective". We from a "Christian" heritage are not alone in this challenge. All of the world religions have the concept of the "return" in one form or another and give various clues for humanity to follow.
I like that you are getting to the essence of the very basis of "belief" and some of the previous comments are in line with my own conclusions. The tradegy in most of our lives is that we want a reasonably quick answer. Maybe just one book or one study class and it would all fall in place. My experiance is that it takes much longer to change one's world view and shed years of accumulated conclusions. Truth, my friend, is in deed, relative and I believe if sought with diligence will manifest itself to any and all that persue it.
carmel