Are they given? Is the name recognizable? Is he/she associated with an educational institution or organization? Has this person written a lot on this subject?
Searching their name in Cameo, WorldCat, PittCat, the Carnegie public library catalog, or Amazon will tell you if they have written anything else.
See if they have written any articles for or are mentioned in Grove Music Online.
Try searching their name in Google.
Look for University Press books.
When was it published? Is it a revision? If it was published a while ago, does it make the information less valuable? Does currency matter to your topic? In general, recent is better (last 20-30 years). Think before quoting books from the 1920s, unless you're focusing on a historically embedded idea.
Is there a preface or foreword? Bibliographies? Table of Contents? Index?