Agreed on all points mentioned previously.
The only thing I would add is if you do the Postal Money Order, DO NOT send it via regular mail, send it either Priority Mail, Express Mail, or at the very least Registered Letter with a signature required on delivery, if undeliverable then the person has to go to their local post office to pick it up, show ID and also will get their pic taken by all the cameras there.
All this can be tracked online at the USPS website, that way you can print the tracking/delivery information as proof if something does go wrong.
I personally would not send anything worth monetary value to a PO Box address, if that is all that is provided from the seller to send the payment, I would back out of the deal no matter how much I needed the item.