I offer a flat rate for shipping because every painting is shipped on a case-by-case basis using the best carrier available for the best rate. Usually, I lose a little bit of money on shipping, but this also ensures that I can ship as safely and as quickly as possible. I err on the side of safe delivery.
Watercolors are shipped in wooden frames with plexiglass protection on the front. These are meant to be a temporary solution, frame-wise, but it saves you from having to rush to find a "final" frame and offers significant protection.
Paintings on canvas can be shipped mounted at a higher price or they can be un-mounted and shipped in a mailer tube (small pieces are always shipped mounted, in a small box). The advantage to shipping them mounted is that they are ready to hang. The disadvantage is that a larger box is... bigger. The advantage to shipping them un-mounted is that it's cheaper and safer. The disadvantage is that you have to have them mounted before you can hang them.
My prints are fulfilled by a third party printer and are shipped in mailer tubes by them, typically by USPS.
For original artwork, I cannot offer a refund for damaged, lost, or stolen pieces. Make sure the gods don't despise you before placing your order.
If you'd like to return a piece because you suddenly decide you hate it, you have to return it in person (in New York City). I won't accept casual returns of original artwork. To do so would be insane. What kind of sicko does such a monstrous thing?
For prints, I accept returns as long as it's done within 30 days of receipt.