I believe this kind of thing happens with some frequency at Amazon. I've seen more than one uproar at GR about Amazon pulling certain erotica titles and they are often ones that include things like non-con and incest. I've even seen publishers use this as a selling point. "Too hot for Amazon" and things like that. Yes, the readers should do a better job reading the description, but on the other side of that, they might've been buying based on other books they read and enjoyed by the author and it never occurred to them in might be "twincest."

I've actually read a different book by this author that was pulled due to content (or so I've read around the interwebz) so the author is probably familiar with this type of thing and took her chances by putting this one on there. (For the record the only reason I read Beyond Complicated was because of the controversy, so I don't think it's always a bad thing.) I believe that book is now available on Amazon since she re-published it, hopefully it doesn't get banned again.

Thank you for your comment. You gave me a lot to think about. Amazon has the right to remove books that don't fit within their guidelines. The author/publisher who submits a book must adhere to those set rules. I feel that I was naïve thinking that books must be approved to be put on Amazon. It must receive a vast number of books each week. So, even if the author/publisher didn't think that their submission was offensive. The majority readers who bought the book did. Thank you again for giving me a different prospective.
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I'm not usually offended by any content (short of instructions on how to commit criminal acts or abuse or glorifying pedophilia) being listed; I'm sure "offensive" is very subjective to each reader. But, if something is offensive or taboo to me, I just won't read it. If misleadingly listed/categorized, I might point that out.

Amazon's guidelines are way too vague. Granted, their site so they'll do what they want to anyway -- but too vague. Kobo actually spells it out in good detail. Provided it's the author (or their authorized agents, publishers, etc.) making that decision, I don't mind sites that want erotica behind 18+ warnings with customers choosing to see or not.

Not offended by book content (nor do I think books about taboos, fetishes or any "kinks" mean that anyone reading wants to try everything in real life or will be "converted" away from their real life morals/beliefs/desires).

I did flag once some bookcovers that I thought, due to clear depiction of full frontal nudity and explicit sex acts, either legally had to be behind "must be 18 to enter" warnings, have little black bars covering bits or that might have been completely illegal because cover models looked way underage. Not thumbnails I thought 13 year olds should be seeing down in the readers also enjoyed section when looking up middle grade gaming books.

Got an interesting response from amazon support that if it was a published cover it was allowed. Yet book content clearly erotica that you only read deliberately gets censored (as opposed to not censoring thumbnails of those underage porn covers, some of which depicted explicit sex acts and if models were not underage they were depicted as if) ... books with similar topics and similar explicitness and taboo levels in a series will see amazon remove some books in the series but not all ... they're very uneven in what they censor.