Does such a thing even exist? If so, is it documented? Who's in charge of it, who invented it? In point of fact, no such thing actually exists. Some of us may follow guidelines put out by one site or another. Some of us may review for sites that have their own guidelines, whereas others are out there flying by the seat of their pants.
I think most of us are trying to spread the word about great and not so great books, and great, or not so great authors. If that IS the case, then why oh why, are we attacking each other? There have been a few dust ups recently and I have stayed quiet because I don't want to be a drama queen, (it takes too much time away from reading), but also because I don't want to hurt anyone's feelings. (Be aware that I'm not going to name names today, because the post to which I am referring has been deleted.) However, today I AM going to lay out where I stand and if you like it, great! If you don't, please feel free to unfollow or unfriend or whatever you feel the need to do. I'm not reviewing to make money or take in advertising (though if you click the links in my reviews I do make a small cut). I'm reviewing because I love books. The only thing I ask is that you please read to the end before you make the follow/unfollow decision.
I feel passionately about a reader's right to review. When I say passionately, I mean it. I don't feel like a reviewer OWES the author anything. If I spent my time reading the book, I have earned the right to say whatever the hell I want to say. For me, this pertains to any reviewer, no matter what their day job is, and that includes being an author. If you read the book, say what you want to say, however you want to say it.
I don't have to be helpful to the author by offering ways for them to write a better book. I am not their beta reader. I was not hired to give helpful criticism or to do editing.
I don't have to be respectful to the author. If I think the book is a piece of junk, I have the right to say so. I don't owe Stephen King or David Morrell respectful words, nor do I owe them to any independent author.
I do not think it's right to jump on another reviewer's review space and tell them how wrong they are. There are one star reviews out there for my favorite book. I don't take the time to tell them they're insane. That's THEIR review space and they're entitled to it.
I do think it's okay to respectfully comment on how disappointed you are that they didn't care for the book, or why you disagree with their review. Again, it should be respectful and not filled with comments like "You're an asshole if you don't like this book."
All of these things said, my personal canon requires that I be respectful in my reviews. I know authors work hard and I know that negative reviews can hurt. That does not mean that all other reviewers must go by my canon. If you're a reviewer, go by your own personal canon. You do you.
I also do not review many books negatively. Why is that, you ask? Because if I am not enjoying a book, I will not continue to read it. I go by a 10-20% rule and if I am not enjoying it by that time, it's out. I have too many books to read to force myself to go on. If that involves an ARC from a publisher, I DNF it and explain why, with no rating or review. If it involves an ARC directly from an author, I will message them, tell them how I'm feeling and DNF the book with no rating and no review. Am I now telling you that's what you should do as a reviewer? No! You do you.
My personal canon dictates that I support other reviewers, whether or not I agree with them. I will support you against attacks from the author or from other reviewers. I can only speak for myself here, but it's important to remember that we ALL are only speaking for ourselves. There is no one reviewer or one reviewing site that speaks for all of us in the genre, (in my case the horror genre.) Not one of us controls what you say in your review, or whether or not you should review at all. NOT ONE OF US. We all have our opinions...and you know what they say about those.
Please note, that if you write a negative review, there is a chance, that the author attacks you, or if it's an author with thousands of followers, they can organize an attack against you. These things have happened and will continue to happen. All we reviewers can do is support each other and stay vigilant. (#HaleNo) But we shouldn't have to support reviewers against attacks/essays/monologues from other reviewers. I WILL, but I shouldn't have to.
This is my personal canon. Are you required to follow MY personal canon? No, (though in the case of attacking other reviewers, I highly recommend it), but again, you do you. I will respond as my personal canon requires, by unfollowing or unfriending, and by expressing my support for the reviewer.
In short, (too late!), I feel a reviewer's space is sacred. That is at the top of my personal canon. Am I asking you to do or feel the same. No!
YOU. DO. YOU.