Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
When a book is in the Wish List, but cannot be downloaded, except for the sample, it is almost undoubtedly, because you have not bought the book yet.
(A Wish List is basically a shopping list.)
The exception to the above is, when your Kindle has lost its internet or WiFi connection, perhaps. Check on that, and try again, then assume that you have not bought the book yet.
Let me know how that goes, please. Thanks.