M4 - I've been preaching this for a few years.
There are 2 legal categories for liability regarding shipments, and they become important to this discussion. It comes down to FOB Dock or FOB Destination.
When you buy something & pay the shipping, you take legal possession of the item at the SHIPPERS location. FOB Dock.
When you buy something and THEY pay the shipping, you don't take legal possession until it arrives at your location. FOB Destination.
Consequently, it is my believe that if you buy mags from a guy in Utah, and YOU pay the shipping, you legally own those mags once he gets the money, and he is simply returning your property.
It just as if you were vacationing at the folks house in Arizona and left your mags behind. Nothing illegal about them mailing your own mags back to you, is there?
Beyond that, the seller in Utah or Arizona isn't bound by Maryland law, only you are.