Of course, authors also have to ensure that if they are going with a small--sometimes even a large--publisher, that the publisher has some idea of what they are doing. Check out the coverart on their other books before you sign on.
On the other hand, I have heard authors complain about perfectly decent covers because they thought the hero's sword needed to be longer or their heroine was brunette not blonde, or some such triviality. So every once in a while we need to remind ourselves just how bad things can get. Here then, examples of cover art so bad they will make you more appreciative of the cover you got, and/or remind you not to use your own clipart cover: http://lousybookcovers.tumblr.com/