In reply to:
Hmm...he claims everything was in perfect condition before he shipped it. He also emailed me pics before he shipped off the speakers, sub and back of sub and the knob was intact. I guess I'll wait to hear from UPS and then talk to the seller again. Thanks for everyones help. I'll let you all know how it turns out. Maybe I'm too trusting?? It's sad that I even have to doubt that he's telling the truth. What happened to the good old days?
There are a lot of unscrupulous people out there trying to get rid of their abused property. I have been the victim of many such fraud attempts. I have also been the victim of package abuse by UPS and FedEx.
Your pictures and descriptions indicate to me that it was not the fault of the carrier. That sort of precise damage would require a hole in the box at the exact location of the knob. Typically, damage by the carrier is evidenced by crushed corners, edges or stained boxes (left out in the rain).
Although I don't want to accuse the seller, it would be very easy to temporarily affix the knob to the potentiometer for a picture and then just throw it into the bag. Perhaps they lost their grip carrying it, their hand slid and a finger caught the knob, snapping it off.
It is not uncommon for sellers to misrepresent their goods over the internet as pictures are unclear and they can claim that they misunderstood a question or some other excuse. I bought some speakers from an individual and specifically asked if they were the model in Rosewood and if there were any flaws (I even broke down my definition of "flaws" so there was no misunderstanding). They said yes to rosewood and mint condition. I received speakers in cherry and they came with dings and dents (not from the carrier).
Caveat Emptor. That is why so many people just buy new (or factory outlet). Unless you can see it in person or it is coming from a reputable reseller, you take your chances. It is
very frustrating.
With respect to eBay, you have a limited time to leave feedback and warn other people of a fraudulent user. Sometimes a claim can last well past the duration of the time limit. Ebay's solution to that is to simply leave feedback based on the situation before the end of the time lmit. In this case, you make the seller irate and they are no longer cooperative in the claim process. And believe me, you
need them to be cooperative to get a resolution from UPS or FedEx.
I'm not saying he did this, but I'm still having a hard time believing with the minor exterior damage this knob could be in this condition, very strange. I hope the sub actually works once you get it all hooked up.. 
