Nonfiction authors must be conscious of the desire of their readers to gain new cutting-edge ideas or substantiate what they believe or what they are looking for. While nonfiction readers search out thought leaders in a given industry for the latest, greatest strategies and techniques, they also want to know that what they are reading is in fact true and accurate. They do not want facts or statistics made up or created in the mind of the author. They are not looking for content where the facts, content or truth has been modified to suit the goal of the author.
On the other hand, most fiction authors do not have to worry much about adding extensive lists of facts to their works. They are exploring the imagination, expanding on a theme, creating a scenario, building a fantasy world, or crafting a tale. Certainly, they want to sound realistic if they are describing a murder scene or relating to a historic event or geographic location. However, since many people read fiction books to escape reality, they are typically not interested in lists of facts or pages of details coupled with cross-referenced research findings.
So how do you provide the necessary credence to your nonfiction works? Use expert references and quotations. Your sources should be peer-reviewed journals, expert websites, research organizations, educational publications, books, articles and other reputable and respected sources by noted people in the field(s) pertinent to your book topic. Wikis or other sources that may not have been properly vetted by subject matter experts in some cases should not be included in your references; although, you may find references to credible sources listed at the end of some wiki articles.
As a final thought on using credible sources for your quotes when writing nonfiction books; provide enough information about your expert to validate what they said, along with their quote(s). For example, when quoting a forensic expert in a book about some famous murder case, you might include something like, “Medical Examiner from ____ and graduate from Harvard Medical School.” Also cite the entire source (e.g. article, book title or website) in a footnote or attached in the back of the chapter or book as a reference attachment.