If you are already a mass market size paperback book from my shelf with one credit and you order a 2nd book of this size, you may select 3 additional books of this size for free (a 5 books for 2 credit deal). Just make sure you send me a PM with what you want as your free selections. Our home is smoke free and we have no pets, however, most of my books are from outside sources so I do not know their history.