To be clear, Amazon will remove reviews at merchant request when the review is about FBA shipping. Generally, these are bad reviews. A merchant would not want to remove a good review when the subject is shipping.

"This came really fast!" 5 Stars is not a product review, however a merchant would not want to remove it. "The box was completely damaged and destroyed the product!!" 1 Star - will be removed by request if shipped via FBA. As with anything for selling on Amazon, they are not exactly consistent with this policy.