I know that the only way Google was able to get permission to scan books is by keeping parts of the book concealed. I think it's on a per publisher/book basis. Therefore, they're not allowed to sell them either.
I am wondering if the section that's concealed depends on what you searched. i.e., if you know which section you want to view, try searches that are very specific to that section. Just a thought...
Try bit torrent for more popular titles, not that I'm condoning that sort of thing!