Sometimes when you get so many books to read, look at, review, or provide testimonials for, you might have to follow the simple method used by the great Polish anthropologist Bronislaw Malinowski to decide which books are worthy of your attention.
Because he did not have time to read every new book in his field, Malinowski would take each new book he received, open it immediately to the index, and check to see if his name was cited there (and how often). The more Malinowski, the more compelling the book would be. No Malinowski, and he doubted whether the subject of the book was anthropology at all.
I have used this same method when I receive new books on publishing, self-publishing, and book marketing. If my name is not cited in these books--and often, they can't be worth much. If my 1001 Ways to Market Your Books is not mentioned, they are hardly worth the effort to crack the spine. My thinking is very simple: If they do not cite me or my book, they do not know much about the field of publishing and marketing.
You should use the same criteria when reviewing books in your own special field. If they don't cite you, ask them why. And they better have a good reason.