This book is so popular that some are now printing unauthorized copies and selling them online. If you see this book sold as "new" on eBay—especially if offered in quantity—then we invite you to consider the character quality of the seller. Granted, there could be the odd person who purchased one copy and then didn't use it. We have no problem with such a transaction. But that is rarely the case.
These books are probably pirated...unauthorized...illegal. Thanks for encouraging quality and good character by purchasing only from an authorized source.