From Amazon Customer Review Creation Guidelines:
If your review does not comply with these guidelines, it may be rejected or removed.
We are unable to accept the following feedback:
Reviews that are not about the product
Seller & Shipping Experience
– Feedback about the seller, your shipment experience, or packaging is not a product review and should be shared at www.amazon.com/feedback orwww.amazon.com/packaging.
Product Availability & Feedback – Comments about product availability or alternate ordering options are not about the product and should be shared by contacting us.
Reviews that contain inappropriate or offensive content
Inappropriate Content – Reviews may not contain obscenities, profanity, phone numbers, mailing addresses, non-Amazon URLs, videos with watermarks, foreign language content (unless there is a clear connection to the product), or other people’s material (including excessive quoting).
Hate Speech & Offensive Content – We don’t allow reviews that express intolerance for people belonging to identity groups including race, gender, religion, sexual preference, or nationality. Customers are allowed to comment on products and question the expertise of authors, sellers, or other customers as long as it is in a non-threatening manner.
Promotion of Illegal Conduct – Reviews may not encourage or support behavior that is illegal, including violence, illegal drug use, underage drinking, and child or animal abuse.
Promotional Reviews – In order to preserve the integrity of Customer Reviews, we do not permit artists, authors, developers, manufacturers, publishers, sellers or vendors to write Customer Reviews for their own products or services, to post negative reviews on competing products or services, or to vote on the helpfulness of reviews. For the same reason, family members or close friends of the person, group, or company selling on Amazon may not write Customer Reviews for those particular items.
Paid Reviews – We do not permit reviews or votes on the helpfulness of reviews that are posted in exchange for compensation of any kind, including payment (whether in the form of money or gift certificates), bonus content, entry to a contest or sweepstakes, discounts on future purchases, extra product, or other gifts.The sole exception to this rule is when a free or discounted copy of a physical product is provided to a customer up front. In this case, if you offer a free or discounted product in exchange for a review, you must clearly state that you welcome both positive and negative feedback. If you receive a free or discounted product in exchange for your review, you must clearly and conspicuously disclose that fact. Reviews from the Amazon Vine program are already labeled, so additional disclosure is not necessary. Read more about promotional content.
Link to the rest at Amazon Customer Review Creation Guidelines