I buy a lot on eBay and have only had a couple of problems. I say sellers should pack to survive an explosion. I once bought a Lenox snowflake that the seller mailed in a thin cardboard envelope. Of course it broke and I wanted my money back and he was very nasty. Things were a lot looser then on eBay and we had a couple of bad feedback on both sides.
I would say, always be nice and you can be vague about who's fault the damage belonged to.