I would say the answer is D. One should never bet on anything.
But this isn't any kind of a moral to the story. This story wasn't intended to sound didactic, or to judge anyone. It is a humorous account of a man who tricks another man by wasting his time on a story about a third man who was tricked. So, it is a story about unreliability and relativity of stories and people's accounts in general. The narrator came to inquire Simon Wheeler about Leonidas Smiley, but Wheeler, having no information about him (or not being willing to give it away), takes the opportunity to talk about another Smiley, a man who liked to gamble.
