How can one tell the difference between Chidushei Torah and words of a heretic?

I was intrigued by this recent M.Y. question and its answers that suggest that one is encouraged to develop his own chiddushei Torah.

This had me thinking about what Talmud Chagigah 15a-b (excerpt here) relates about Elisha ben Avuya who eventually became a heretic. It relates a conversation that he had with his student Rabbi Meir. Elisha asks him about his interpretation of several verses. Then, Elisha refutes him and gives another explanation that, offhand, sounds valid.

If one were, say, studying with someone else and his friend offered a novel explanation, how would one be able to evaluate if it was valid or the words of a heretic similar to Elisha ben Avuya?

Note: While I'm citing the example of Elisha ben Avuya, please generalize your answer regarding dealing with anyone.