Just whatever you do, don't forget that one negative feedback comment is in no way the end of the world, and you can leave brief explanations for negative feedback.
If the situation is as you've described, it sounds as though you've done everything you can reasonably do. If the guy's being a jerk about it, he'll just have to enjoy being angry for awhile. AFAIK you are no longer under any obligation to him for anything once the packing company has filed their claim.
You could always offer to refund his $550 if he ships everything back to you, but he would still have to pay the shipping charges for both the sale and the return :-D
When you've got positive feedback behind you, one negative comment will rarely (if ever) affect your status as a buyer or seller on ebay.
