At BookMooch.com, you can add books you will send out to others to your inventory. If they match a book someone else wants, that person can ask you to ship the book to him or her. For every book you add to your inventory, you get 0.1 points; for every book you ship you get 1 point; and leaving feedback also earns you 0.1 points. In return, every book you get costs you 1 point.
So far, the site has accounted for about 10,000 books traded, worth about $150,000. That's possibly lost sales for publishers.
How to make a silk purse out of this pig's ear?
Well, offer to give away your book. It might be a good way to get people to sample your book or to build an audience for a new author, whose second book is coming out soon (give away the first book, not the second). It could also be a great way to get rid of excess inventory or hurt books.
