Use Dropbox as a download delivery system for sales.
If you’re starting a business selling downloads like MP3s, images, or ebooks, you can use Dropbox to deliver the files.
Let’s say you’re a keen photographer. A family friend sees your portfolio, and wants to buy an image. You sell the image. It occurs to you that others might be interested in your images, so you decide to offer them for sale. You create a small website, and you make sales. Just send your buyers the links to their purchased images in your public Dropbox folder so that they can download them.
If you're just getting started selling ebooks, use Dropbox.