Proper action for a stolen package from a Buy/Sell/Trade transaction

[Kaneen]

3 weeks ago I made a purchase from a very trusted member of a Facebook collector's group. We had great communication, and I paid immediately via PayPal "Goods and Services." She mailed my package the next day via USPS Priorty Mail in Cincinnati, OH. The package was estimated to arrive at my PO Box address in Lexington KY (approx. 80 miles from the seller's shipping point) 3 days later, on a Saturday.
...On Friday, tracking showed that my package had arrived at the Lexington regional distribution center (nearly always says that the day before I get a package.)
...On Saturday, I checked the tracking before going to the PO to pick it up. Tracking says "Arrived at USPS Regional Facility, Des Moines IA." Well that's an interesting side trip.
...On Sunday, tracking shows it arrived back at the Lexington Distribution Center.
...On Monday morning, the package arrived at the Versailles KY post office (about 20 miles from my PO).
...Later on Monday afternoon, 1:26 PM, the package arrived at my Post Office. PO Box mail at my location is always placed in boxes by 11am.
...At 5:12 PM on Monday afternoon, the tracking now shows that my package was "Delivered, In/At Mailbox"
...Packages too large for the PO Box are placed in a lobby locker with a key left in the PO Box (I get them like this all the time, no issues).
...It is now 2 weeks later and I still have never seen the package, nor the locker key.

To recap...Seller clearly did her part; USPS screwed the pooch; who knows what actually happened to the package? (Probably mis-delivered and not returned by the improper recipient, but who knows); tracking shows "delivered"; ...and I never got the package.

Even if there was such a thing as a Net54 BST "policy" (which Leon says in this thread he has no intentions of instituting), or commonly accepted "board etiquette" (which is clearly not commonly accepted by everyone), there would still be cases where it is just not simple and clear cut.