My understanding is that the post office requires a return address. UPS and FedEx even require photo ID which matches the return address, or at least provides them with a way to track it back to you if you say you are mailing it for someone else. The post office does not yet require that the person mailing the package produce an ID of any type, but they do have the right to ask for a return address., My experience is that they accept whatever return address is on the package. They verify using a national database that the address you are mailing to is correct, but I don't believe that they validate the return address.
When I do Comcast shops, I have to provide a valid service address which Comcast can look up in their database. When I am out of area, I provide an address which "I am thinking of buying." There is a small but finite risk that the Comcast employee lives in the house or next door, but it is the best I have come up with so far. ON one occasion, I even had to find the listing on my smart phone since the Comcast employee was initially unable to find it.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008