Your point about the difference between understanding a teaching and just being exposed to it can be used to defend theists and atheists who try to convince others. The point may be to search for those who have ears to hear. So why should everyone be wary when they see an atheist or a theist talking to them about God? Maybe some are interested in religion so they've studied up on the subject. Certainly, that would be the expectation of readers of Interfaith Now, a website about religion.
I'm glad you're aligned with Buddhist thinking. I respect that religious philosophy or therapy much more than I respect monotheistic religions. But if you believe the self is an illusion, I wonder why you would advise listeners to be wary. What were you trying to protect with your comment?
I wasn't specifically talking about the Buddha, but about gurus and so-called enlightened sages in general. As I understand it, the first records in Buddhism were written several hundred years after the Buddha's presumed death. That's a long game of Broken Telephone. So we don't know much about the Buddha's life in history.
I think it's possible to train the mind to overcome disappointments and other forms of suffering in life. Still, there's a valid doubt about whether anyone's fully enlightened or is at least partly faking it for ignoble reasons.
What's wrong with theories? Haven't scientific theories led to much technological progress?
You might be interested in some of my articles on Buddhism.