I was reading the blog of a friend of a friend and came across a discussion about selling used books online. It sounded like there are a bunch of different sites that buy used books. Each of them allows you to put in an ISBN number to see what they are willing to buy it for.
To find the best price, you would have to browse all of these sites to see who was offering the most money. Sometimes the a book may sell for a dollar at one site, but nine dollars at another, so it is worth your time to check out all of the sites.
Sounds like a good candidate for automation to me. I am already doing a pretty similar, but more complicated, version of this with GamePriceWatcher.com. It didn’t take me much time to write some scripts to scrape prices from about eight of these sites. I also included the Perl WWW::Scraper::ISBN module to retrieve some of the details about the book and it has turned out pretty well.
I have it working now at http://avazio.com/sellbooks.php, and may move it over to its own domain if it seems like anybody is using it.