The book industry is complex. My partner works in a publishing house and it's never easy.
I bought your plug-in, but I am very frustrated.
1- The damn isbn code does not necessarily make the right book.
2- the associated books section are not limited to the default language (French in my case).
3- the Amazon link does not seem to work. I have a link to Barnes and Noble. Obviously, they don't sell books in French, so it's useless.
I also bought your Movies plug-in. It's really awesome! It would be really cool if Books worked so well! ;-)
Thank you for your work.