The Antiquarian Booksellers' Association of America website offers a member search under the Booksellers portion of their website, and users may limit search parameters to local professionals who offer book appraisals. The ABAA website notes that all members abide by a code of ethics and undergo a screening process.
The Association of College and Research Libraries, part of the American Library Association, publishes a "Your Old Books" guide through its Rare Books and Manuscripts Section. This guide, freely available on the the RMBS website, provides a wealth of information on the factors that make an old book rare or valuable and gives advice on steps owners can take to protect, value or sell their items.
Large booksellers such as Abe Books offer appraisers and referrals for appraisers. People who have a rare book or a collection of rare books can easily search the Abe Books inventory to see if a book is for sale or get price information on recently sold volumes.
Owners should also consider the subject matter of their books, as many fall under the category of a specialist. The member search on the ABAA website allows users to limit search parameters to a specialist category, such as gardening, cookbooks or children's literature.