How do you determine the value of an 100+ year old book?
The value of old books varies depending on the quality, location, and the buyer. Depending the age and condition of a book I usually turn to Amazon or eBay as well, due to a much larger display. However sometimes, taking the book to auction house where there is a pre-auction appraisal has worked extremely well. If you are looking to conduct your business online only, you can try the site in the source field which has been quite reliable in the past. Sources: http://www.mindspring.com/~bookdealers/consult.