Well, I think most fake stories are easy to recognize - the writters just write about their fantasies, and from their point of view (after replaying the fantasy many times in their head), they do not realize it is so obvious
. I think they usually do not do it to fool anyone, I suppose just the fact that they made their fantasy "real" by writting it up as if it happened and sharing it turns them on.
Sometimes, I am puzzled. Like - a guy writes a story about how his hot colleaugue or neighbor challenged him, posts some photos of "her" (found on internet) and asks what other thinks, if he has a chance, what moves should he use, etc. I read that, smile, want to hit the back button... and then notice there are several well meant advices. And I wonder - have those guys just accepted his game and play along, or do their really think the story is genuine?