I think last year a similar thing happened to a member here from FL. Their many trades via Pinpics show as "delivered" but they did not get their pins. Eventually, they found out that it was their mailman's mistake.
The packages get scanned upon delivery, but technically it can be delivered anywhere in that zip code. If their neighbor got their package by mistake or something like that, it will still show as delivered. Our last mailman used to deliver our neighbors' mail to us every now and then by mistake. It happened more than once and with different neighbors. So, it is very possible that the package you got delivered somewhere else.
Here are my suggestions:
* Contact Ebay and ask what to do
* Communication is key: Talk to your buyer and tell them that you are in touch with Ebay. Also tell them to ask around with their neighbors. Is this person in an apt? If yes, there is a good chance that this package either went to the apt. complex' office or to someone else's mailbox.
I do not think Ebay/Paypal would fault you and force you to give the money back as you have delivery confirmation, but of course there is a good chance that the buyer might leave you a negative feedback.
It hasn't been more than 30 days either so I don't think you can do this until the 30 days are up but you can also file a claim for a lost package and the post office will go investigate it. Maybe it will turn up that way?
This is a good idea. Sometimes the post office gives you the usual run-around, but hopefully with some luck you will get help.
I am sorry to hear this bad experience Marcia, best of luck.