There are plenty of reviewers who review despite conflicts of interest. These include well-regarded review bloggers who also offer editing services, and review bloggers who also sell author PR packages. Conflict of interest doesn't automatically mean unethical. Presumably a reviewer could ignore the fact that they are being paid (or have been paid, or will be paid) by that selfsame author to perform a different duty. But it is a conflict of interest, irrespective of claims of special safeguards.
Many reviewers are ethical, yet useless. They don't seem to have any standards. Amazon "Top Reviewer" Harriet Klausner is an infamous example. She reviews ten books a day, awarding most of them five stars. To be fair, in the early days of Amazon, she was a prolific, but legitimate reviewer. In the 1990s, I got the feeling she even read the books she reviewed. I doubt she reads them now. Another mass review source on amazon is Midwest Book Review. They award only five star reviews. 65,000 five stars to date. Can all 65,000 of those books really be extraordinary?
Outright scammy reviewers abound. These include the amazon "sock puppets". A sock puppet is an author who gives herself a five star review, often under a fake account. I recently read about an author who had given himself three five star reviews (out of nine reviews). The author was outed on the amazon forums, and suddenly two of the three fake five star reviews disappeared.
Reviews by family and friends are both useless and scammy. Here's a typical one:
This book is really really good. I couldnt put it down. I read it so fast cause the words just flow and I had to know what was going to happen next. Highly recommond this book. Awesome is all I can say!!! ;0)Such reviews are pretty easy to spot because there will be a cluster of them, all posted within a few days. The reviewers will also have only reviewed that one book. Evidently no other book was as awesome!!!;0). Some authors will arrange review exchanges with other authors: if you give me a five star review, I'll give you a five star review. I consider this unethical. These reviews are often well-written, and are harder to ferret out as fake without doing some cyber-sleuthing. Fake review determination is truly a science. But if a book sells a few copies a month, yet has 51 five star reviews, you can bet the author is gaming the system.
The author who has no friends or family can always buy a fake review. Only five bucks!
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