That's a very good question. The answer is that it depends.
1 John 4 warns us about false teachers and false prophets. A true Christian teacher/prophet will agree that Jesus Christ is God; that He came in the flesh. If they agree with this, they are true followers of Christ. They don't necessarily need to know every scripture to perfection. We are all learning.
However, if they teach that Jesus was not God come in the flesh, then they are not true followers of Christ. They can be charming, witty, intelligent, and soft-spoken. None of that matters. They do not believe in Christ if they deny he was God in the flesh.
1 John 4:1-3
1. Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world.
2. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, 3. and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already.