Jossik and God books
Currently when speaking to Jossik he will mention that he is willing to sell you a new Damaged book for 100,000gp, or exchange one for another book.
However when you agree to buy a book he will instead open a shop interface and sell Damaged books of their respective gods for 200gp each.
After a bit of research I found that according to Tip.it's archived Prayer guide the following should be the case:
When you've completed your first book (all four pages of the related god), you can go to Jossik at the first floor of the lighthouse north of the Barbarian Outpost and get another book of a different God. You need to have your first book completed though; he won't offer to sell you a new one unless you have the other(s) completed. A new book will cost you 5000 gp.