is a book review a violation of lashon hara?

My wife sometimes writes book reviews on her blog as well as on the jblogbookmom’s blog and a recent e-mail she received gave rise to some halachic consideration. After offering some critical comments about a new book, the author e-mailed back that offering such negative comments violates hilchos lashon hara and may cause a loss to the person’s parnasa. Additionally, in this case the proceeds of the book are directed to tzedaka, so by causing any diminution of the book’s sales the tzedaka indirectly suffers. There were other comments in the e-mail explaining the reason for the author’s umbrage, e.g. the author claims the book was written for altruistic reasons – as far as I can tell, altruistic intentions are not a substitute for actual writing skills, so I'm not sure what the point there was. But the halachic question is at least interesting – is a religious author or artist protected from receiving a critical reviews of his/her work because of the laws of lashon hara? I find this idea hard to swallow. By the author’s reasoning there is no place in the Jewish world for restaurant reviews (who would eat at a place where the food is bad?), reviews of cars, clothes, travel, etc. (who would buy inferior products?), or any discussion of whether a product has merit because if the answer is negative, the producer inevitably suffers a loss of business. Never mind the fact that such a loss may be deserved or that the consumer bears the brunt of supporting what may be inferior goods or services that he/she would never have purchased had he/she known better. I think what the author misses is that the author or producer’s gain has to be balanced against the to’eles of the public being made aware of the quality of a work so they may make an informed decision as to whether to invest time and money in it. And while to a certain degree reviews are a matter of subjective taste, a reviewer should be able to defend his/her arguments for or against a work with examples, analysis, etc. There is a big difference between a statement of opinion with no justification and the type of critical review one might read in the NY Times or London Review of Books (and I guess I take for granted that my wife’s writing is closer to the latter than the former!) Secondly, it seems to me that anyone who makes a statement in the public arena through a work of art, a book, or some other medium implicitly surrenders his/her right to immunity from reasonable criticism. That is part and parcel of exposing one’s opinion to the world, and I think it inherent in the gemara’s principle of “chvrach chavra is leih”. Lastly, the loss of tzedaka funds is nothing more than a red herring – no one purchases a book simply because the author has pledged proceeds to tzedaka, and no impediment to buying the book stops someone from writing a check to the tzedaka if they wish to support it. Is a book store obligated to carry the book in question simply because not doing so restricts the possibility of funds going to a tzedaka? So much for my rough thoughts on the matter – I wonder if anyone has written up something more formal on the subject?