Read this book and you'll be skeptical, from then on, that the "extra virgin" olive oil that you buy is really "extra virgin," or that it is even olive oil completely--or at all.
I didn't read the book, but I listened to the audio all the way through. It was an eye-opener.
Extra Virginity: The Sublime and Scandalous World of Olive Oil, by Tom Mueller.
Rated 4.5 stars at Amazon; 3.91 at GoodReads (a little low there, even for GoodReads--you might want to read the reviews).
Now only $1.99--only 12% of the digital list price!
https://www.amazon.com/dp/B005LW5IZ4/.