Agh, yes. I saw a book today in which, according to the blurb, the entire point was that the heroine was far from beautiful in a world that prized beauty above all. So what do we find on the cover? A very beautiful girl. I did much mental ranting about how this reflected an appearance-obsessed society (presumably publishers think that plain girls don't sell books). However, it's probably nothing to do with any nasty agenda, but is just the usual situation of cover illustrators not bothering to read the book. (Though it's probably not their fault. They're probably writing to a lazily-written brief.)