Adding the page numbers where they'll find the information makes it more than just a sales pitch but guarantees that it's in the book waiting for them. (myworkfromhomemoney.com)
You can also add a page of reader testimonials (used with permission). (pressbooks.com)
Some of the recent changes are fairly harmless, like adding a page for your account that lists every app you have ever bought. (goodereader.com)