you are under no obligation to replace delivered merchandise.

First red flag: thieves aren't going to stand there on a porch and open a box of merchandise, leaving the empty box behind.

Also, the post office will not deliver a compromised package without a sticker stating that the package became opened within the postal system.

Let the buyer know you will contact the US Postal Inspector to file a theft report to see if they can help and you will get back to her in a day or two with their findings...that often thwarts these scammers and they will 'find' their package ("the postal person just found the item in her truck...blah blah blah"...yeah whatever...go away now).

You can actually file a missing package inquiry on the USPS website and I recommend doing so...often i get feedback from the post office about a particular address having repeated delivery issues ("Tell her to check her Ring doorbell video", one post office responded), or they will speak with the recipient directly ("the carrier spoke to the recipient, as the package WAS delivered"), etc.