I've read novels where the cover illustration had little to nothing to do with the story, as if the artist-designer asked "Give me the gist of it,"
then knocked up an illustration using stock images. One crime novel showing a moody lake on the cover had only a dried-up stagnant pond in the plot, and another about a disappeared child, who may have been kidnapped, or she could have run away, featured a discarded tricycle and teddy on a pathway, neither of which appeared in the story.
Reading the newsletter from the excellent Book Designer website
, I understand from what owner Joel Friedlander says, that sometimes designers read the book before creating an illustration, while other times they depend on a brief synopsis.
The best example of a customer taking revenge on false advertising occurs in Falling Down
, when Michael Douglas as a rejected and frustrated defense engineer seeks sustenance in Whammy Burger (I won't be doing this in my nearest bookshop or library!):