Comments: The HDD apparently got damaged in shipping, and I asked Dave to test it with multiple cables, to no avail. I simply refunded the money, and he was okay with the situation.
He was very patient and understanding throughout the entire transaction, and was willing to do anything necessary to try to either revive the HDD, or take a video of it to show me that it really is dead.
So in the end I just let it go and refunded the money.
Still, I'd deal with Dave again in the future. Thanks!