Even "free shipping" is not free. The price is built into the sale. Therefore both the pickup and the final delivery are customers.
....and every package is not something bought or sold, but we in every instance sell services of varying levels to the shippers.
Therefore the shipper is who we have a commitment to satisfy under the terms of the guaranteed services contracted.
Many times the packages do contain purchased goods, but sometimes they contain documents, gifts, personal items, etc.
Hell, sometimes the shipper is the consignee.
My point, for the sake of this discussion, is who cares?
Just follow the methods and get a signature if required, whether the lady on the ring doorbell begs you to forge her name and leave it on the porch, or not.