Find the book's colophon either at the beginning or end of the book. This will list all of the information you need to evaluate the resource.
1. Evaluate the publisher.
A University Press means it is scholarly. Not a University Press? Google the publisher to learn more about them. There are some academic presses that are not affiliated with Universities like Routledge.
2. Still not sure? Evaluate the author's credentials.
Consider whether or not they an academic or expert in the field.