Having your friends and acquaintances read your work and writing a review is not unethical. Your circle is your first source of word of mouth. Does it make sense to tell them NOT to read it and NOT to write a review, even if they like it?
I think it's against Amazon's rules to do that.
FWIW, anyone who has had a kindle for long is leery of authors frontloading the reviews for their books with 5-star reviews from friends and relatives. I've talked to many on the Amazon forums who simply refuse to buy a book that has nothing but 5-star reviews.
Other patterns they look for (and I look for too):
1. Ripping on the reviews of anyone who gives less than 5 (sometimes even when people give less than 4!) star reviews.
2. Mischaracterizing any negative (or even neutral) reviews as personal attacks and petitioning Amazon to remove them.
3. Marking as "unhelpful" any negative or neutral reviews so as to move them off the book's first page ASAP.
4. The usual five-star glut comes right about the same time the book is released; even on the same day, suddenly there are 9 five-star reviews.
5. The rave reviewers have only a single review, and it's coincidentally for that one book. Often a cluster of such raves are posted within an hour, or even within minutes of each other of each other -- like the result of robo-reviewers all getting sent the bat signal at once from someone's blog or by cc'd e-mail to hurry up and get a rave review up there.
6. The reviewers are robo-reviewers -- likely part of a paid group or a reciprocal group of reviewers, who post ONLY 5-star reviews (is it even possible to always love everything?) and more likely than not haven't even read the book. Sometimes these groups have dozens or hundreds of reviews up, sometimes dozens in a single day. The system is vulnerable, unfortunately, to the corrupt.
7. The reviews have no substance. "Trust me, this is a great book! Don't wait, put it in your cart now!" or "This book swept me off my feet! I wish I could give six stars!!!"
Gaming the system isn't something that's done a different, unrecognizable way each time. People are used to it by now, and it makes authors look bad.
What's really amazing is when authors start fighting back. Google "author's big mistake." It's a huge mistake.