... such as it is, is nicely appraised by Scott Esposito: Trusted Fellow Reader.
I think that readers develop a sense of which reviewers they can trust. It isn't that they necessarily agree with them, or immediately run out and buy every book they recommend or scrupulously avoid any they dismiss, it's rather that they feel they've got a fair appraisal - and can take it from there themselves.
Because of space constraints, I usually tell reviewers that if they really don't like a book, don't bother reviewing it. Find something you like that you can tell readers about. I also think positive reviews are more heeded by readers than negative reviews are. Moreover, a good reviewer tells you enough about the book and his reasons for liking or disliking it that you can make up your own mind about it.
My column, Editor's Choice, is designed for recommending books, so I rarely have the opportunity to write negative reviews. Tomorrow will be an exception, since I was asked to look at a couple of European-bred Da Vinci Code clones. I was underwhelmed.
Again, much has to do with the tone adopted. Dale Peck's tone is pretty narrow-gauged. And a lot of people seem to have adopted a snarky manner in order, I guess, to get across how tough and tough-minded they are. I've been around the block far too many times to be impressed by that sort of thing (and also for reasons indicated in this post). In fact, it turns me off.
If anything ought to be an example of a civilized manner, it's book reviewing.