I tell people how I ship and sell my cards but nothing beats seeing it, so here's an example...

When you get one of my artcards I don't just mail the card. It comes sealed in a protective plastic baggie just like a comic book bag. Just.. um... card sized. Then I slide it into a thick acrylic case with really rigid edges to make it very difficult to bend.

I'm sure that if you really tried to damage the card in the housing you could, but the packaging protects it from a lot of accidental damage like being dropped or briefly getting wet or such.