When I go booking, finding a book with an author autograph usually insures a sale, but that sale can depend upon condition. I don't ever purchase books that have water or mildew damage. On my last booking trip, I found two books by Carole Nelson Douglas which contained not only her autograph but a brief message to the original owner and the paw print of Midnight Louie, the cat who acts as the detective in these works.
One of these works also had an owner signature which I was able to sand to good success. Again on sale of such a book, this removal should be mentioned.
Catnap is the first book in Douglas' Midnight Louie series. This tends to increase the value of the book although not as much as books may increase in value because they are an author's first work. When I am booking, I take both of these facts into consideration when making a purchase. A f/f of Catnap sans autograph is valued at about twenty dollars while a nice autographed copy is selling for as much as fifty dollars. Personally I like the fact that Carole Nelson Douglas chooses to personalize her autographs rather than just flat signing her books. I also like the paw print that she has added to the Midnight Louie books.