There are many types of books written for many different purposes:
Click this link and take a few minutes to bowse this PG Library eBook. Pay attention to the information on the detailed record page, including the Abstract and Details information, as well as the Full Text link on the left of the screen.
Things to consider:
After browsing this item, can we trust that it passes the criteria as a credible publication? If answering yes, then chances are it is a source of credible information. If answering no, then you may want to consider an alternate source.