this book may help you.
First of all, I like the structure of this book because it uses Gap Model to connect the content of the whole book. At the begining of this book, it first introduces the importance and tools of service marketing. Then it chooses Gap Model to divide this book into different parts. Under different gap problem, the book shows the ways to close the gap. I believe this structure helps to understand more easily and relate what should be done under different problems.
Secondly, many diagrams are used to describe the concept under service marketing. Service blueprint in the chapter 6 is a good example. It uses diagrams to explain how to draw, how to read and how to use the service blueprint. It is very clear and useful to explain in this way.
However, there are still some drawbacks. For example, when talking about the different kinds of strategies used under service marketing, sometimes the explanation is too simple and not in depth.