It is not reasonable to hold set of doctrines x, in contradistinction to doctrines y, based upon a shared appeal to the Scriptures, in that the dispute alone demonstrates the appeal not dispositive. In English: Neither man has any reason to believe that the Holy Spirit is not speaking to him. So either God is lying or in error, or this isn't the way to figure out what God said. Pretty simple, but you actually have to consider in humility that the other guy might not be Satanically deceived, simply because he disagrees. If you see this in good faith often enough, you'll doubt not God, but this hermeneutical method.