How to change Amazon’s book recommendations to Kindle Editions
If you buy a lot of Kindle books at Amazon, you may want to have Kindle Editions of the books suggested rather than print editions. It’s about what will appear in a section Customers Who Bought This Item Also Bought.
You can easily change the settings.
1. Go to Improve Your Recommendations page.
2. In a left sidebar find Edit Your Preferences widget and check the box (see picture below). Done. Since that time Amazon will recommend you books in Kindle format.

Picture 1
Alternatively, you’ll be given an option to improve recommendations after you buy a Kindle book. You’ll see an alert like this:

Picture 2
Any time you can go to the Improve Your Recommendations page and return to old settings by unchecking the box.
Pingback: Kindle Tips: 15 Tricks & Tips to Get the Most of Kindle Store