A bad review can seem devasting to an author, but in truth, it may not cause much harm.
This is from a journal report in Marketing Science:
"Crunching data that cross-matched book sales against critics’ appraisals in The New York Times Book Review, they found that negative reviews of a new book by an “established” author hurt sales.
“For books by relatively unknown (new) authors, however, negative publicity has the opposite effect,” increasing sales by 45 percent over their expected sales trajectory, they write. Evidently this boils down to increased awareness: the mere act of introducing something to a broader public — even by saying that it stinks — increases the chances that more members of that public will want it anyway."
So cheer up friends, and remember to offer to review books for fellow writers.
I write book reviews professionally, and while my reviews are not always five-star winners, I almost always get a thank-you from the publicist, and often, from an appreciative author.