Marketing is promotion!  To promote a book, good things about the book contents, yourself, your family (if genealogy) or area (if research tool), and history, as well at the physical form the book takes will be pointed out. These are all selling points.  Don’t overlook something that is positive because it wasn’t the main publishing focus.  For instance, archival quality is becoming a much talked about and sought after element in reference book publishing.  Whether this was of high priority for the author personally, it may contribute to sales if it is publicized.