There are a gazillion websites that help authors promote books. Why would bloggers and companies help you promote books? Because they are affiliates of the retailers. They get paid every time someone clicks through a link on their blog/email and goes to a website to buy a book. For example, Jose is a blogger. He hosts a website called ‘Jose’s Bargain Books’. Every day, he posts information about books that are on sale. Some readers visit his site daily, several thousand get emails from him about the books on sale. When those readers see a book they like, they click Jose’s link and find themselves at the Amazon sales page for the book. Jose will get a percentage (usually anywhere from 1%-4%) of whatever the reader spends at Amazon, whether they buy the recommended book or not. Jose gets a ‘finder’s fee’ just for sending the person to Amazon—even if they get to Amazon and decide to buy a toaster instead! This is called affiliate marketing, and it is how Amazon became Amazon.