Q: How could a reader check to see if a writer did extensive authentic research prior to writing a nonfiction text?

A: You could check the bibliography, but I prefer a simpler method.

Look at the photograph of the author on the back of the dust jacket.

If the author looks serious and distinguished and professorial, he probably conducted extensive research.

If the author is giving you the finger, he probably has little respect for you and did minimal research.

If the author looks like Jennifer Love Hewitt, you can be sure that no research of any kind was done whatsoever.