The author is an expert in their field. Check their credibility by looking for details about them via a Google Search, try and locate a CV, or ask your Professor if they're familiar with the author's work.
What institution(s) or organization(s) is the author affiliated with?
Have they authored other publications in their field?
Note the publisher of the book; often university press or professional organizations publish scholarly content.
Are references or works clearly cited? Does the text contain footnotes?