Amazon.com does this with great success. You can see a portion of any book through their “Look Inside” promotion. You can do this on your own sales page but creating an excerpt of your book with the title page, author bio and one chapter (with a call to action to buy the book at the end). Instead of just allowing people to download the excerpt ask them to sign up for your newsletter or “notification” list so you can keep them up-to-date on discounts or new books. This is a great way to build your list.