Yep, I think the only defense against someone criticizing an unboxing video is to sit near your front door on the expected delivery day, recording device in hand and finger on the button, and as soon as you see/hear the delivery driver pulling up, start recording and don't stop until the device is unboxed. The sheer absurdity of anyone actually doing that is what works in the favor of scammers on both sides (buyers and sellers).

Another thing I do is only buy from and sell to people with 5+ years and 50+ transactions of feedback, and at least a few transactions at the same dollar value that I'll be doing with them.