There have been quite a few articles corroborating the existence of books like this, the only part that needs believing is that someone actually used the books as advertised.
Even if you doubt this particular case (which I haven't seen any reason to do), it's inevitable that people will believe some of the things they read in legitimate looking books sold by major online retailers.
Of course the story remains plausible, and it certainly has an air of truthiness, but I'd give it very good odds for being fake.