I wonder how much this actually harms the author? I really do not know what the typical deals authors have with publishers. Obviously different authors have a wide range of leverage with a publisher. But if an author is somewhat established aren't they usually given and advance against future sales? I ask because I dunno...
But, while these retaliatory/"guerilla" reviews might not harm the author for a given book, if such reviews appear in sufficient number to lower the rating then it will harm the author come time for the negotiation of their deal for the next book because the publisher is going to point to lower sales numbers for the last book even if a reason for the lower sales and ratings might be due to the business practices of the publishers. BTW, if all publishers actually make this the norm I would expect whatever authors guild/union to look into collusion charges, though the courts today simply have made it too easy for companies to collude even in the face of there being obvious proof of acting in concert and in an anti-consumer fashion. I mean look at cable and the telco's (especially cellular) companies and how all of they rates change in concert and their plans never are truly competitive.
So, in a way the publisher wins no matter what approach the consumer takes...to me that is one of the things I find wrong with publishers (or record labels as well) in that they point fingers at both consumers as well as use anything they can to pay the author less. I really hope their comes a point for many authors where they have enough success to be able to contract with an editor, an expert to create well formatted versions of the book in however many formats the author chooses and of course someone for any cover art and in book art. Because of the ability to self publish this can be handled all outside of the publisher's reach.
but, I just don't know who well or poorly publishers treat most author.
Still I see a setup similar to how one can pick up contract programming jobs on any number of sites where the developer bids on the project. Such a system is really great for both parties because if things go well, odds are there will be more work should the developer want to keep working with the individual or company, but if either party is not pleased, both can move on with little or no hard feelings until they find the right people they can work with successfully.
Still I feel the consumer is the loser if these sort of reviews become the norm as peer reviews were once an excellent source to gauge a product. These days with angry "getting even" reviewers combined with paid reviewers, the systems are becoming less relevant every day.