DR Woody - libraries use jobbers like Baker & Taylor and Ingram and others as our wholesalers. Sometimes, our acquisitions department has to go directly to the publisher, but tries to minimize that because it's always more expensive. We use Amazon more in the selection process, looking for "reviews" and such. We put more stock in reviews in professional journals and the mainstream press, like the New York Times Book Review, but for opinion like you'd overhear in a bookstore, online is a great source.
DR George may want to add to this discussion - he works more in the acquisitions area than I.