[DocTomoe]

Making it dependent on bookstore.org immediately cuts off international users. I'm not taking a transatlantic flight to "buy locally" - and the prices local bookstores ask for importing books are laughable (often three or four times the prices Amazon asks).

Sure, you could mention the ISBN, and I could manually go to Amazon, and find the thing, and buy it ... but what a hassle to me as the user just so that you as the site operator can make a political statement.

I would invite you to consider doing some geo-lookup of the user's ip address and provide alternative integrations.