One is that the book shall not slop over into the real world too nastily. I can remember reading Jerzy Kosinski's _The Painted Bird_ when I was a kid, and being edgy about being near members of my physically harmless family for an hour or so--just because they were human beings. I swore that I'd never read anything by Kosinski (seeing the movie of Being There doesn't count), and, while I don't take that sort of an oath seriously--not after decades, I haven't gotten around to any of his books since.
Another is _The Name of the Rose_. There's no way to go into any detail without spoilers, but let's just say that it's not a conventional mystery novel, and I was expecting one.
Now that I think about it, the Kosinski thing isn't exactly about the contract as usually conceived--that's about genre--it's more about what I expected from books generally.
When have you guys gotten really angry at an author for how a book affected you?