My guess is that anyone who purchases this volume will be interested in making portraits that will reveal the person photographed and perhaps, to use an art school phrase, show his or her soul. This book will not do that. At most, it might give you a few tips that could make your pictures more attractive. However I really can't recommend this book to anyone.
Some photography instruction books set out a few key principles and then develop techniques from them. This lets you form a picture in your mind of what you want and then manipulate the environment and your photographic tools to create that picture. Unfortunately this author doesn't develop the kind of approach to posing that would help you pre-visualize a portrait and then adjust the sitter's pose to fit that concept. Instead Wacker bombards you with a number of small rules that you may have to keep reviewing regularly unless you have great recall. He says "don't keep people on flat feet; don't show women's knuckles; turn the body plane away from the camera for a thinner look". At the other end of the scale the author frequently reminded me to be imaginative, involved and open to learning.
The book is organized into three parts: the psychology of posing; the mechanics of posing and posing in practice. The psychology section seemed rather elementary but adequate, emphasizing points like building confidence and getting to know the subject. What should have been the meat was contained in the mechanics section. For example, there's a chapter on posing tools, in which the author discusses such items as adjustable stools, stepladders, carpet pads and posing tables. But I didn't learn anything about how to use these tools or when one might be more appropriate than another.
I found the section on posing in practice very frustrating. This part is organized into chapters on children, high school seniors, men, women, etc. Most of these chapters offered advice that didn't help me. For example the chapter on women admonished me to pay attention to details they (presumably the author means women) find important, be sensitive, place the body to emphasize gracefulness and femininity, and build excitement.
Some photographers might pick up a point or two from Wacker that will improve their portraits, but I'm certain the average photographer would learn more about posing from any good general portraiture book. I certainly found that I learned a lot more about posing from the book "Professional Secrets of Natural Light Portrait Photography" by Douglas Allen Box, which doesn't even purport to be a posing guide. Unless you really need a book with just posing tips, look elsewhere to become a better portrait photographer.