One thing the trades maintain—and an informal survey of freelancers bears out—is that reviewers are not directed to take a position on the books they're writing about; instances in which a reviewer's judgments are overwritten by editors are rare. Which means this: For better or worse, a motley assortment of underpaid and often anonymous reviewers using their own unfettered judgment have a great deal of influence over the books you are most likely to come across in your neighborhood bookstore and, if you are shopping online, buy.
Adelle Waldman, "Book Report: How four magazines you've probably never read help determine what books you buy," Slate (15 Sep 03). The anonymity is a problem. So is the warrant for the assertion that "instances in which a reviewer's judgments are overwritten by editors is rare." There is instead the subtle pressure of future assignments; editorial expectations are usually at least implied to reviewers with each assignment.
On the other hand, it's probably better than the obscene sycophancy of movie reviews. Nothing to aspire to, but not as bad.