If you are trying to sell more books, create more value for customers.
How do book sellers do that?
Find book lists. Examples are The 100 Best Business Books of All Time and the Personal MBA book list [77 books]. When a customer is looking to buy a book on these or any other list, included should be any lists the book is on. Some books are on more than one. Provide each. Then ask this question...
Are you interested in any of the other books on the list?If the customer indicates they are, the book inventory database can instantly pull all the titles available. This can create an extra sale and save the customer a bit on shipping and handling. This is like cross merchandising categories in the supermarket [EG: Peanut butter and jelly near the bread].
Make it easy for the customer to do more business with you. Doing so will deliver more value. Customers love value.
Are you asking your customers how you can delight them more?
Better yet, are you asking yourself how you can do this?