A lot of false teachers started off really well then sort of lost their way. Often it seems to be with fame and the reverence of their congregation that inflates the ego. As soon as their flock no longer question anything they do, watch out. Every cult has a leader who is unquestionable. What I have noticed though is many people who may preach a very flawed doctrine have often written some brilliant books, usually earlier on in their ministry but not always. We should always remind ourselves that preachers are human and very flawed and not expect perfection and when they fall, watch how they act/repent and see how they will remedy the situation. One of the worst is K P Yohannan from Gospel for Asia, a missionary organization that had such a good concept but again, lost their way. They obviously mismanaged/stole enormous amounts of money yet their leader has not admitted a thing with all the evidence condemning him. Thankfully though most are very humble after getting caught and can go on to have a better ministry than before if we'll just let them. And we should.
Also its important to take most of your Christian influence from text. The chance of someone saying something wrong is so much greater than them writing something wrong as it will be checked and rechecked before publication or posting (you would hope!).
I'd like to add to that list J John. He has a most unique take. And though he's long gone one that stands out is Merlin Carothers who had a most unique take to adversity and tragedy: Welcome it all because only be accepting everything can we let God work His wonders to full extent. His premise is God is most willing to help if only we didn't get in His way! And the only way of doing that is accepting the misfortune at the time, which, when really awful, is very challenging. For example, not many parents could welcome the death of a child but as they can't bring that child back, by welcoming that event, brutally tragic as it was, they allow God to make the most of the situation. And isn't that the whole point? Maximization of opportunity? Isn't that all that anyone can do in their short life? Given the choice we all would lay down our lives if many others could be saved because of it. Its only natural in the grand scheme of things. Our time on Earth is a brief moment compared to our eternity in Heaven.