It's been suggested, and voted plausible, that Amazon may be using a setting or application that uses the Facebook links provided on your Amazon Author page to scan your Facebook friends list and determine their decision on "you know this author personally" when allowing/disallowing reviews from your readers.
Does anyone really need to see your friends list anyway? No!
Of course, we can all sign the petition asking Amazon to change this policy (and it's doubtful they will), but, in the meantime, why not make it more difficult for them to use your friendships/followers against you, right?
How to lock down your friends list:
This must be done from a computer or the "desktop site" setting on your mobile device.
If you're unsure if your friends list is currently view able, check it out on step 2 first.
Step 1: First go to your timeline and click friends (see photo below) and enter in "to edit" section and "manage" your friends as per your conditions. (I set mine to friends for all the options here)
Step 2: Go to settings, click on "timeline and tagging", "view as", click on your "friends" tab, and see if it shows your friends/followers. If it's locked down it should say "no friends to show."
Step 3: Rejoice knowing you may have just saved yourself from getting one of those notices from Amazon refusing your review! Either way, your list of friends is now safe from prying eyes. This is good.