Hey Runningbird,
If you're going to sell the book and want to make sure it's high quality, I've heard that often times you can contact the author directly and ask for a review copy. I haven't tried it yet, but I've had several people tell me that they don't mind giving out copies to their affiliates, because they really want you to be an affiliate - they want people selling their stuff.
You'd still have to actually read it, of course
Which you should, because it seems like 99% of the reviews out there are really thinly veiled sales pitches from affiliates!
The other option is, if you're someplace like Clickbank, you can buy through your own affiliate link to get the discount, and review it that way. I was just reading a thread on this, and *most* authors don't care if you do this - although one or two get upset. Most just see it as another sale...
Of course- the best option is to write your own ebook, so you know it's high quality - and then get other people to sell it for you
!