For some time, I have been reviewing books (and other things) as part of the Amazon Vine programme, and I've given the whole subject a lot of thought. I thought it might be helpful to other writers to share some of the things I have discovered.
1. Beware the one-off five-star review. If a review is (usually) an ecstatic, five star review, and the writer of that review has only written one or two (or no) reviews before, the odds are that this is a friend/famly member of the author. This may be fine, but it probably means that the writer is trying - with the best intentions - to be kind, but the review will inevitably be biased.
2. It is better to have more reviews, with a wider range of ratings. After all, not everyone will enjoy our work, and it's fine for readers to say so. It at least means someone has read the book, and taken the trouble to review it.
3. Especially beware the reviewer who tries to promote his/her own book through the review: ie "Review by ANNE CLEVER-DICK, author of MY WONDERFUL NOVEL". I came across one of these yesterday. The review is not about you, Ms. Cleverdick. It's about someone else's book.
4. Never write a highly critical review using the name under which you write. Pay-back is only a matter of time, and you may well find your own book slammed by the author (and his friends).
5. If you can get a top reviewer to read and review your book, so much the better. All reviewers are rated by Amazon.
I have experienced all these things - including the ecstatic relatives - and you may already know all this. But I thought it was worth saying (forgive me if I'm stating the obvious in this post).
Cautionary tale: ages ago, I approached a publisher with a view to asking them to look at a book of mine. I received an amazingly forgiving email saying that "as I had just reviewed one of their novelists under the heading 'Where, oh where, was the editor?', she declined the opportunity to read my novel". Oops. I apologised profusely, and she was so gracious that I really wished I could have had her as my publisher. It was quite clever of her to trace me as I review under a different name.