I have committed this sin myself, a couple of times--once, when I was a teenager, when I think it could be excused, and once when I didn't realize the person (a fellow LJ'er) was actually a professional writer; I had thought she was just an extremely dedicated amateur.
Any fan who wants a writer to read his manuscript or introduce him to colleagues should read what Scalzi has to say about the matter. My feeling is, if you want to be a writer, then write, and write, and write. Then submit, submit, and submit your work. You have to put in your ten thousand hours--at least.