They can't, because the beta is on the disc - you download the beta as part of the game's downloadable content, when it hits. I think people will start selling it once A) they don't like it, or B) they didn't want to have to wait for the beta.
Kameo was ok, I suppose. Not the kind of game I'd go back to after completing, though.
Off topic (Actually on-topic, for a change): I was thinking that it might not be a bad idea to reorganise this thread, delete all the posts bar the first one and have that display the gamertags of everyone so far. It'll get rid of the pages of Halo 3 and Crackdown discussion that do well with its own thread.