Unfortunately, some self-published books are like a more formal looking version of the National Enquirer, but from my personal experience it's easy to tell the difference. Henry Baum, the editor of Self-Publisher Review is a great supporter of self-publishing and thinks that many of best self-published authors are aiming their books towards marketing a product or service. To me, that makes perfect sense. Marketing Managers are experts in the marketing field, as well as the field of the product or the service that they are trying to sell. As experienced Marketers they probably have very impressive written communication skills, which makes for an interesting read. I think that marketing by means of books is a really exciting new phenomena. If you're curious about services that a company offers in a more detailed complex fashion, a book could supply that information for you.
As a student having these books available is also a great resource to read and see what other services companies are doing, and a chance to see what their outlooks are on certain situations. Robert Skrob, President of the Information Marketing Association talks about his opinions on the benefits to a business writing a book in an article on the About.com website. He thinks that it is a great tool to advertise for all different kinds of businesses. All in all I don't think that non-fiction self-published books will really sell unless the author is somewhat specialized in the book's topic. For authors writing about their product, service or business, whom are obviously specialists in their own self-publishing opens a lot of doors when it comes to marketing.
