As others have said, "customer damaged" is very common. I think I've got maybe 8 items in Unfulfillable right now as "customer damaged". You'll have to manually request them to be removed and sent to you, pay some minor fees to do so. The status of these items once received really varies. As others said, a good chunk of the time, they're totally fine and they just get re-stickered and sent back in. Other times, well, they look like the attached image -- and you might have some luck getting them reimbursed but it's tough.
Generally, I just chalk them up as a loss and hawk opened sets on eBay, sets that no longer have a box and are missing parts go into our own personal parts inventory, or find some other use for them. It sucks, but it's a cost of doing business. Most importantly: if you're going to send them back in, be really sure they haven't been opened, parts replaced with something "similar" and "resealed".