Well, if you notice, a good deal of self-published books have amazing all 5-star ratings. That's because these people get all their friends to rate the book. You'll notice that a lot of traditionally published books have fewer stars... is it because these books stink? No, it's because they're LEGITIMATE reviews from people who don't know the author.
I think that this "author" is just doing it to stand out among all those self-published, all-5 star books, because (as some said above) people WILL want to read it to see how bad it really is. The market is so glutted with crap, people are doing anything they can do to stand out. I beg of you, save your money and buy a REAL book... there is plenty of badly written crap on the internet that you can read for free!