In what way would a previously unbiased observer determine which of the scriptures was indeed inspired by God? I don't know. I think, however, that he wouldn't be able to use the revealed words themselves, because that would be circular reasoning.
And then you have the fact that all four of the revealed words of God has been found to have inconsistencies.
I think it's best if we don't stick dogmatically to any of them.
Indeed! It is SO EASY to shut people up from criticising you when you invent a crackpot religion by simply CLAIMING INSPIRATION FROM GOD!
Watch the TV preachers who have "received a word" from the Lord!
How do you refute somebody's "word from the Lord"?
An honest person would say, "I've got this crackpot idea I want to foist off on you..."
But, hey.....that's not going to happen.