The worst book cover I've ever had was for A Woman of the Iron People. A woman in a low cut dress, who appears to be southern European, possibly Carman or the gypsy in Il Trovatore who throws the wrong baby in the fire, holds a human or hominid skull toward us. The woman is not in the novel. As far as I can remember, no one in the novel ever holds a skull.
I asked my editor about the cover. It's been a long time, and I'm not sure my memory is clear. But I think I remember him telling me that my heroine was nonwhite; and in those days -- 1991 -- it was common wisdom that you couldn't put nonwhites on the cover of an SF novel. So they put someone else entirely on the cover. I assume she was holding a skull so readers would realize that the book was anthropological SF; and maybe it hinted at death and violence, always attractive in a novel. I assume her bosom was falling out of her dress, because it was common wisdom that SF is read by boys and young men.
Karen Axness at A Room of One's Own in Madison had to beg customers to buy my novel, because the cover was so repellent.
This year at ICFA David Hartwell explained to me how such covers happen. He was not talking about Woman, but Melissa Scott's Shadow Man.
You hire an artist who has done good work in the past. He turns in something ghastly; and you don't have money in the budget to commission a second painting. So you go with the ghastly cover, even though an intern with a Mac could do something better for free.
Well, that is one explanation, and doubtless it is true.
There used to be a cataloger at the Hennepin County Library System here in Minnesota. His name was Sandy Berman, and he was interested in how cataloging can be used to control information and make sure that unpopular information cannot be found, even though it is in the library, readily available to anyone who can figure out how to find it. Sandy had a national rep and the respect of many librarians, but he was not popular with his bosses and was finally pushed into retirement.
In any case, I keep wondering -- sour person that I am -- if novels are sometimes sabotaged more or less by accident, by making them difficult to find. Any number of people can do it -- the editor, the artist, people in marketing, buyers at chains...
The editor is the least likely suspect. Why would he sabotage a book he's bought? But the book's survival is dependent on so many people, and so dependent on fitting into the right slot.