The only way you can know whether or not a human teacher is teaching truth is if the Holy Spirit of Christ reveals that to you. In fact, the only way you can know scriptural truth is if God teaches you by His Spirit. And these truths will never contradict the Scriptures. Any other knowledge of truth is, at best, only an intellectual assent. Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him.
Time is short.