Anyone ever dealt with a C.O.D.?

I'm a mailman. The way COD works is this. We come to your home, knock on the door and tell you that you have a COD package. You pay the mailman, he leaves the package.
part of the COD charge is for the purchase of a Postal Money Order.
So if the package is $100 then the PO will collect $104.00.

Yes the carrier likely has a PS 3849 (the salmon colored slips) pre-filled out. We are under a huge time constraint. So we generally don't hang around long. I give a door 1 knock or 1 ring of the bell, then I move on. You can come to the Post Office the next day and pick up. I'll accept cash, but only exact change. If you hand me 2 $100 bills, you'll get them back and be told to come pick up the package. Same as with a credit card.
Now, if you decide you don't want to accept the package, then it's returned to the sender. As far as you being the buyer, it's great. No harm no foul. If the you see the package is visibly damaged, refuse the shipment.
If your a seller, there is the danger of losing money on a refused package. and you have to wait until delivery to get paid.