Free Book Previews
The TV Shows section of Google Play has an area where you can watch the first (pilot) episode of popular TV shows. The same happens here but for various books that are currently available.
The goal is to offer you a slice of the beginning of a book and then hope that it interests you enough to want to finish it. Naturally, you have to buy the book to finish it but this is a great spot of the Play Store where you can browse through available books.