I started selling on-line at bdsmbooks some years back. The editor at the time was convinced that the 'harder' a title was, ie, the nastier, the better the sales. I had my doubts, but he was always pushing me to write nastier material. So some of my titles, especially earlier ones, can be nasty and totally non-consensual. They often focus more on the pain and humiliation of the female protagonist than her pleasure and heat. None of those books can be sold on amazon because of their content policies.
Now I haven't run into any censorship at other sites, that is, Smashwords, and the places it sends my books, like barnes and noble or Diesel ebooks. Still, I'm not convinced the quality of those earlier books is up to par, and so I haven't tried to sell them beyond the hard core sites they're on now. Amazon, of course, has kicked or denied almost all incest, so those books can't be found there. Likewise, Amazon will sometimes reject a book for God only knows what reason. They won't tell you why, just point you to their content guidelines, which are exceedingly vague. I had a book denied a couple of months back, and after an email exchange with amazon was still baffled by why. I wound up changing the cover and title and resubmitting, and this time they took it without issue. Was it the cover? God knows. You'd think if it was the cover, at least, they'd tell you. I had another book refused last week. Again, no idea why. There was no nudity in the cover, and no non-consensual sex or incest in the story. I've got a new cover and title and will try again. Meanwhile, the book is selling on smashwords, doing well.
I did have an email exchange with a bdsm publisher who said that in his experience if book has the word 'rape' in it, it's more likely to be banned, even if there's no rape involved. Since a number of my books have role playing and 'verbal domination' that word can certainly appear, as it did in this last one. "Ooo, are you going to rape me again, you nasty pervert?" But sometimes I suspect it just depends on which reviewer looks at your book. I know they don't actually READ it. But I'm guessing some are quicker to say no than others, perhaps because they're more prudish. If anyone has a better theory I wouldn't mind hearing it.
Btw, despite their annoying censorship policies, amazon does pay the highest royalties, so if you're looking to buy an ebook I'd prefer you buy it from them. :) I do the same. I saw an intriguing looking novel for sale elsewhere the other day, but went to amazon to purchase, knowing the author would get higher royalties there.