B.M.
I don't think you are being unreasonable at all. I sell books on amazon.com and recently had a similar incident with a buyer. Unfortunately the book never made it to him. It was poor shipping (I didn't tape it enough).
I have found that the post office is often to blame regarding these issues. If your envelope had a stamp that showed that they received it in poor condition, I would call the post office and file a complaint (I have friends who work at the post office and they have suggested this).
The seller should do *something* to make you happy.
I hope it all works out.
B.
btw, I love that you say that you are constantly telling your boys to keep their hands to themselves. I only have 2 boys and I probably say it at least 20 times a day!!