3 out of 5 rating for Pathfinder Roleplaying Game: GameMastery Guide
This is "Gamemastering For Dummies", a book of tip and advice for how to run a game in Pathfinder. Much of the content is generic, and works for other games with a similar narrative structure. That is, this book would probably work less well for games with more of a narrative structure, like Fate. But it does say Pathfinder on the cover, so that is not a weakness.
Overall the advice is sound. There are few surprises here for for an experienced gamemaster, but there is a lot of moments of fond recognition and every reader will likely get a few epiphanies. The book is also reasonably structured, so if you have a specific problem you want a solution for, you can probably find it quickly.
This is a fluff kind of book, it has a few rules near the end, but these are neither particularly important or particularly good. The drug rules in particular seem written more to teach kids not to do drugs than to actually be a serious game option. This is not a book you'll need to the game session, and perhaps that is its greatest weakness; if you can borrow this book to read it that is generally quite sufficient. Still, as the latest in the long series of reference books for gamemasters, this has a niche to fill. Newer GMs will find solutions to a lot of problems in here.