I have noticed a particular pattern with popular books on Amazon.
A lot of them have quotes from the press highlighting how great they are.
The positive reviews, especially the "Most Helpful" ones often make out the books to be the best they've ever read, which is suspicious. Also, these top reviews tend to be very long and detailed, but all in the same way.
When you write a negative review, sometimes you get an unusual amount of "Unhelpful" votes.
Sometimes the same books have the same amount of reviews on amazon.com and amazon.co.uk.
A lot of the positive reviews seem fake. Some will be positive even though the reader states things like they haven't read it yet.
I don't trust positive reviews in most places.
Also, Amazon now has it so you can only browse the latest popular books, rather than the most popular. It's impossible to browse for an old popular book unless you know its title. It isn't censorship exactly, but certainly limiting on purpose.
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I've left WP.