I understand your predicament, as a lot of sellers, myself included, will not ship USPS. Standing in line at the post office for an hour to ship one box is not an option...
I'm not sure I understand. You can print postage paid labels online at USPS
. Once you do that, your mailman can accept them, or you can drop them off at the post office without having to stand in line. In my experience, USPS ships the fastest and is the cheapest. They even give you free boxes.