In the auction was it shipping? Or shipping and handling? Was insurance offered? Did you accept or decline insurance? If he offered it and you declined then its your loss if something happens to it. I give you the point that he should have offered a tracking number to you, but he probably had some way to track the item. I just shipped a package to Canada didn't ask for tracking, and the clerk pointed it out to me. I know anytime I send stuff back to manufacturer's I am automatically given a tracking number.
In other words.... if the sub is 100% ok, works perfectly, wasn't damaged, doesn't rub, etc. etc. Then I say let it go, don't buy from him again, or ask him/her to package the product better. Its pretty gey to get the sub you want, at a good price, and then leave negative feedback or even neutral feedback if the product still made it to you in a timely manner and in working order. If the sub is screwed up, then that can go to the part about insurance...if he offered it and you declined then the ball is on you, if you paid for insurance and he didn't provide it then the ball is on him.
I say maybe you send him a message saying his packing could be better and maybe offer some tips on how to improve it.