Lost package.

[yodipuppy]

Buyer didn't receive her package but the tracking number said it was delivered.  What happens in a case like this?  It was a pair of shoes.  I don't want to refund the money because I will have lost the funds.  But the post office said it was delivered and could she be just saying it wasn't delivered just to get her money back.  What does a seller do in a case like this?

[ebooksdiva]

If your buyer has opened an item not received case upload tracking into the case for seller protection. Many sellers think because you bought the label on eBay that it will automatically be attached to the claim, it doesn’t work like that. 
If tracking shows the item is delivered to the buyer you are covered, you don’t owe the buyer a refund. 
It is the buyers responsibility to ensure a safe location for their items to be delivered. 
Tell the buyer to check with family or neighbors that may have collected the package. 
If they still can’t find it, your buyer should then contact the police to file a report and if their homeowners or renters insurance covers theft or property from mail boxes report to them as well. 

[soh.maryl]

A seller politely tells that buyer that tracking shows delivered so there's not much you can do to help her.  She has no way to get a refund in that situation.

You need to do a little more reading about the Money Back Guarantee and what it does and does not cover.