Goodreads Librarians Group discussion

The book links, for the most part, use the identifying number on the edition you are looking at.

In the case of the link above, this edition is the ebook with an ISBN. Since Amazon uses ASIN numbers, it does not recognize the ISBN number - which is why the link doesn't work. If you were on the page of the Kindle Edition, the link would work properly.

The links are customised by the user so they choose bookstores they want see on the buy links