How Librarians Choose the Books They Buy
According to writer Joe Konrath, "libraries do their ordering from catalogues supplied by the publisher, by catalogues supplied by the distributors (Ingram and Baker & Taylor,) and through reading reviews in Library Journal, Kirkus, PW, and Boolist, plus others. Patron requests and word-of-mouth also are a factor."
Konrath provides a detailed description of his marketing campaign targeting these librarians at his blog, A Newbie's Guide to Publishing, in his November 21, 2005, post. It's worth the read.