One book-shipping mistake that seems small but can get expensive

Publishing the book is the hard part. Then you realize you actually have to ship it.

Books can easily get damaged in transit. Corners get dinged, covers get bent, and moisture can become an issue. A lot of the time, the damage doesn't come from the shipping carrier itself, but from books having too much room to move around inside the package during transit.

It's one of those details that doesn't seem like a big deal until you're dealing with replacements, refunds, or a disappointed reader. So it's really important you have the right book shipping box for it.

If you've shipped books directly to readers, what's a shipping lesson you learned after your first few orders?