Amazon reviews, Part Three: Who qualifies as a reviewer?

There are serious book reviewers. There are jerks who simply give a book a thumbs-up or a thumbs-down, as if a book were something like a pair of boots from L. L. Bean. There’s everything in between. When I ask, who qualifies as a reviewer, I really mean, who qualifies as a serious reviewer?

I’m talking about reviewing fiction. Memoirs (too often close to fiction?), history, biography, technical, scientific, etc. are less likely to be questionable as long as the author of the review is objecti...