So, our friend has the same ISP and has High Sierra. He has no problems with the reviews.
Well, the problem now appears to have been narrowed down to something within your four walls, so let's go for the one remaining opportunity for failure of which I'm aware: clearing cookies (which has never been mentioned, so I'm guessing that it hasn't been done).
First do a command-option-E; it will clear cache and make the list with which you've got to work next far less cumbersome.
Now go to Safari > Prefs > Privacy > Manage Website Data... and delete not just Amazon items, but every item that hasn't got the name of a website that you ordinarily visit.
Quit/relaunch Safari.
Holding my breath!
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
