You could start with this article.
I've decided not to accept free books from the CSFF blog tour anymore, since we always link to amazon.com, and that makes it linked to "seller"--and an advertisement, I guess. I'll only buy the books I want to read and skip the rest, as I have done, anyway for a year plus. I hope publishers will start to make electronic manuscripts available for review. Those we can delete, hence, not be "compensated."
Would be easier on my eyes, too.
I wonder if those reviewers who get free books and only gush and give 5 stars (maybe 4) without any real criticism will be under more scrutiny...