Box-O-Books is a subscribable feature that lets you swap books for books with other members, and no credits are needed.
Why use Box-O-Books?
It saves you money! Sending multiple books in one shipment costs much less in postage than sending single-book shipments.
It saves you credits! When you don't have any credits, you can still get books!
This service is especially useful to new members; they can swap whole boxes of books with other Boxers, thereby replenishing their library while waiting for their newly Posted books to be requested and earn them credits.
Box-O-Books is the only way that PBS members are permitted to swap "books-for-books" without using credits.