I always thought the "Take everything as truth or in good faith" was more about the fact that it's really difficult to truly figure out if something is fake or not and if you start enabling people to declare stories fake, then you risk ostracizing the OP and people that are thinking of posting similar stories.

As well as it helps prevent needless discussion over the text. It just seemed more sensible to make the decision to wash your hands of it and not think too deeply about it than let the comments go wild arguing with each other over the story.