This was on Amazon.co.uk, as far as I can tell, but the principle would apply to Amazon.com. It is not only possible, but quite easy for someone to review anonymously. It is both courteous and ethical, of course, to identify any connection one has with the book. For example, an author or publisher reviewing his or her own work anonymously would be wrong. I think we all know that.
But in this case reported by AP (via Google News), the author’s wife gave fairly nasty reviews to he husband’s colleagues and very favorable reviews to him. No doubt, one spouse should love the other, but perhaps this is going a bit too far. And the extremely favorable review of her husband’s work was pretty revealing–and stupid.
Two lessons: 1) Take anonymous reviews, accusations, and so forth with discernment and 2) Always identify any connections you have to the production of a work if you’re going to review it.