q - Search for volumes that contain this text string. There are special keywords you can specify in the search terms to search in particular fields, such as:
- intitle: Returns results where the text following this keyword is found in the title.
- inauthor: Returns results where the text following this keyword is found in the author.
- inpublisher: Returns results where the text following this keyword is found in the publisher.
- subject: Returns results where the text following this keyword is listed in the category list of the volume.
- isbn: Returns results where the text following this keyword is the ISBN number.
- lccn: Returns results where the text following this keyword is the Library of Congress Control Number.
- oclc: Returns results where the text following this keyword is the Online Computer Library Center number.
Click image to enlarge
As you can see, in the above image, querying the Google Books API using the :isbn parameter returns more managable results, however as this query shows, ISBN's aren't perfect; this particular result returned different books with identical ISBN's. It is something that cannot be helped, but can be overcome with good design. E.G. Allow the user to select their book from a short list of results.
Conclusion
Basically, from reading into both API's I can see that Google's will be easier to work with and is a lot more flexible. Amazon's API is huge and thus complex - I'd spend half my time reading the documentation before I could do anything useful. Also, when you register Amazon require you to declare that your app will promote their products; I would have to twist the truth to manage my registration with them. A relevant article about Amazon's business ethic surrounding their API's for mobile use can be found here: http://techcrunch.com/2009/07/07/amazon-killing-mobile-apps-that-use-its-data/.
I have chosen to use the Google Books API to support my application.