Clicking on a reviewer's pen name takes you to their Amazon profile containing biographical and other information they've posted about themselves. Some reviewer profiles will explain what types of books they prefer. For example, some reviewers stick with fiction; some review only movies or music. Some profiles indicate whether the reviewer accepts unsolicited books, and some provide a postal or e-mail address.
But Amazon gives you a way to reach reviewers who don't display any contact information on their profiles. At the top right of the profile page, click the link Invite to be an Amazon Friend. This generates a pop-up form where you can enter a message, and Amazon will forward it in an e-mail. This maintains the reviewer's privacy, and if they aren't interested, they may simply ignore your message.
A soft-sell approach works best when approaching Top Reviewers. Offer a complimentary book in return for their considering to review it, no obligation. Most Top Reviewers don't want to commit to a review until they've seen the book. Don't ask reviewers to return the book.
Here's a sample script you might use to approach Amazon Top Reviewers:
Dear John Doe:
I got your name from the list of Amazon Top Reviewers. I've written a book, "How to Grow Organic Strawberries." I noticed from your Amazon profile that you frequently review gardening books. If you think you might be interested in reading my book and posting an honest review of it on Amazon, I'll gladly send a complimentary copy if you'll reply with your postal mailing address. There is no obligation, of course.
Best Regards
Carefully screen out reviewers whose profile indicates they aren't interested in your book's topic. For example, don't send your fiction title to a reviewer whose profile says, "I review only nonfiction."
Some Amazon Top Reviewers make it a practice not to review a book from a new author unless they can honestly recommend it to others and give it a rating of at least three or four stars out of five.
Only a small portion of Top Reviewers are likely to respond to your offer. Some are inundated with review copies from publishers who already have their mailing address and know their reading preferences. Other Top Reviewers are skeptical of books sent directly from authors, after having received poorly written self-published books. Some busy Top Reviewers disable the Amazon Friend invitation system by adjusting their profile's privacy settings.