Every time I leave Cyseal town the stores seem to restock for me, even when I stay on the same map and do nothing else in between.
A vendor in Cyseal has walk in the shadows book for me but I don't need it because I started the game with it on my rogue.
I don't believe backstab is a book. Its an ability (like leech/opportunist/pet pal etc) and once you have it you just go behind an enemy and the attack cursor will change to the backstab one if you are in the right position.
