My package is slated to be delivered today, yippee! I'm going to call them tomorrow to confirm that someone has received the phone and ask when a refund check will be issued and how will I be notified.
As far as the proof of purchase and activation on an account, I was never asked for either one of these. I did tell them that I purchased it on CraigsList and that when I went to activate it on my account with Sprint customer care over the phone they told me that the phone was no longer being activated on their network. Also when I asked for a refund they originally said $849.99 + tax, but the latest that I heard was $879.99, not sure if that includes tax or not, so we will see what will come back to me.
I shipped back a brand new device, plastic still on it with it never being activated or a call timer tripped. If for some reason they begin to give me a run around I will add that representatives name to my notes and begin to pursue other means to receive my compensation and then some.
**EDIT** Got paranoid, called Samsung (extended wait, I guess from being in the middle of the day) and they confirmed that they received my phone. Said I should expect to receive a refund check by 11/30, and if I did not to call back and they would escalate the issue. Also confirmed that I did not need to send in proof of purchase or activation on my line, but if they refund check will be for $849.99 and if I did have a receipt they would include the sales tax. So at this point the response that I'm getting back from them is making me happy. She did also say that I may receive my check sooner than that date, but that would be the latest. I also expressed that I just want to make sure I receive a check and she said some checks have been received.