Have You Added Your Bookstore to AddAll?
AddAll.com is another service that provides a central search for consumers when they’re looking for used and rare books.
You can suggest your online bookstore to their service here: Suggest Bookstore
One a user does a search, it will display the results. When the consumer decides to purchase the book, they are then directed to your site in order to complete the transaction.
I don’t know if this is a free service for booksellers, but it is definitely worth taking a look at. You know me, I can’t see having more people looking at your inventory as a bad thing 
