I have seen a lot of blogs lately about reviews-- whether evaluating the worth of reviews, how to decline doing a review for a writer if you don't think the book is good, or if you should review something you really think is terrible and how far you should go with the review.
Reviews don't sell books. According to a link on the Sisters In Crime website, a study was done and reviews were not in the top three things that cause someone to buy books- unlike reputation of the author, word of mouth, and price.
However, I am of the opinion that a book review, whether good or bad, can drum up interest in your book. If a website only has six followers, and just one of them decides your book is worth buying, that can result in multiple sales if they end up liking it, because this goes back to word of mouth. One person likes it, spreads the news, others end up buying it based upon the first person's recommendation. I don't mind sending a free book if the review is actually going to appear on a blog or someone's website, but I will check out the blog or website first to make sure books are actually being reviewed, and to check out the quality of the reviewer's writing before submitting.
That being said, I received a luke warm review from someone who will remain nameless, who although found fault in my characters, particularly the protag in Gumbo Justice, also said I had promise and to buy the next book when it comes out. What a mixed bag of tricks that one was. But everyone is entitled to their own opinion, and I'm sure there are books that didn't impress me that others thought were the bomb, so I'm not going to argue.
(I feel the same for movies, such as the whole Twilight thing. I love vampires-- the way they're supposed to be, menacing and scary, not cute and romantic-- and found the whole concept and movie dull and slow and the acting kind of horrible. But that's me, and most of the world apparently disagrees, go figure.)
In any event, I have received a nice review from a blog where I did send the reviewer the book, and she really seemed to enjoy it. I feel like she'll likely buy my second when it comes out, and if a few people who read her blog do the same, I've made some sales for the cost of one book. Being a first time author, anything that gets my name out there is gold. (The blog is at http://conniesreviews.blogspot.com/2010/03/gumbo-justice-holli-castillo-2009-oak.html if you are interested.)