Any system that is important enough to be measured is going to be gamed by cheaters, and Amazon's reviews section is no exception to that rule.
Amazon has fought back by suing over fake reviews, deleting reviews where the buyer appeared to have a relationship with the author, filing for arbitration against scammers, and putting a cap on the number of reviews you can post without buying the product.
Now Amazon has revised its reviews policy yet again, this time to target scammers who open new Amazon accounts just to post a review.
To contribute to Customer Reviews or Customer Answers, Spark, or to follow other contributors, you must have spent at least $50 on Amazon.com using a valid credit or debit card. Prime subscriptions and promotional discounts don't qualify towards the $50 minimum.
It's good to see Amazon continue to fight scammers, but I don't know that this will have much impact. After all, a scammer can always buy the products they were hired to review and then charge their clients for a verified review.
This is basically a game of whack-a-mole, but fortunately, this time around authors won't get caught up in Amazon's fight against scammers.