Let me introduce you to a new feature at How to Publish in Germany: the “EBOOK-DATA” section. The software that also provides data to Selfpublisherbibel.de regularly looks at Amazon.de and creates a database of e-book sales data that you can easily search on the site.
How many books did a certain author sell? How did sales and price of a book change with time? How many ratings are there, and what’s the medium rating? There is a lot to be learned here. Data is already available for upto two years back. And it’s free, of course.
Data for other German e-book-stores is coming soon.