Where is the volume discount?
The US Post Office policies are very strange regarding my orders. Since 9/11, any package weighing more than a pound must be taken directly to the post office clerks; one cannot send them from home. This means that I usually send each multiple book order out one book to a packages to avoid driving to the post office and standing in line. And even more strange, the cost of sending them goes UP per book if they are sent several books to a package. I've tried many times and am still amazed that sending four separate packages is cheaper than one package with four books.
Also, books and CDs have a mailing option called Media Mail, which is quite cheap, but the service is so inconsistent that it's pretty much unusable. For the first several years of sending out books and CDs, I used Media Mail, but every so often an order would take months to arrive. Usually I would have already done a free re-send, only to have the buyer notify me eventually that they did finally get the original order and now they have two books!