From Amazon’s TOS:
Promotions and Commercial Solicitations
In order to preserve the integrity of Community content, content and activities consisting of advertising, promotion, or solicitation (whether direct or indirect) is not allowed, including:
Creating, modifying, or posting content regarding your (or your relative’s, close friend’s, business associate’s, or employer’s) products or services.
Creating, modifying, or posting content regarding your competitors’ products or services.
Creating, modifying, or posting content in exchange for compensation of any kind (including free or discounted products) or on behalf of anyone else.
Offering compensation or requesting compensation (including free or discounted products) in exchange for creating, modifying, or posting content.
Posting advertisements or solicitations, including URLs with referrer tags or affiliate codes.
The only exceptions are:
You may post content requested by Amazon (such as Customer Reviews of products you purchased on Amazon or received through the Vine program, and answers requested through Questions and Answers). In those cases, your content must comply with any additional guidelines specified by Amazon.
You may post an answer to a question asked through the Questions and Answers feature (but not a question itself) regarding products or services for which you have a financial or close personal connection to the brand, seller, author, or artist, but only if you clearly and conspicuously disclose the connection (e.g., “I represent the brand for this product.”). We automatically label some answers from sellers or manufacturers, in which case additional disclosure is not necessary.
You may post content other than Customer Reviews and Questions and Answers regarding products or services for which you have a financial or close personal connection to the brand, seller, author, or artist, but only if you clearly and conspicuously disclose the connection (e.g., “I was paid for this post.”). However, no brand or business may participate in the Community in a way (including by advertising, special offers, or any other “call to action”) that diverts Amazon customers to another non-Amazon website, service, application, or channel for the purpose of conducting marketing or sales transactions. Content posted through brand, seller, author, or artist accounts regarding their own products or services does not require additional labeling.
Book authors and publishers may continue to provide free or discounted copies of their books to readers, as long as the author or publisher does not require a review in exchange or attempt to influence the review.
For more information and examples, read About Promotional Content.
There is a lot of discussion many places about the disclosure on reviews and, yes, you still need it. Please note that not only will it not save your Amazon reviews but it will make customers distrust any review you post. And any author who encourages this.
Like this one.
Then she sort of leaves it up to the reviewer:
I know she has been evacuated because of the hurricane so hopefully when she returns home (may it be in one piece) she will find her misplaced good judgement.
Add the disclaimer. If you lose a review on Amazon, it’s just words. If you don’t disclose and people find out you’ve been receiving books you review for free, well, you might lose their trust and that is something a lot more important than any review.