Unless they fund the payment with a credit or Visa debit card a buyer cannot get anything back, id they open an item not received or not as described case you just need to tell ebay or Paypal that it was a pick up sale. It is important if you have invoiced with postage that you reinvoice without so it counts as not being delivered.

If they have funded with a card then they can try doing a bank chargeback and just llike the buyer has no protection neither do you the seller so you need to create your own. A copy of their driving license scanned onto a collection receipt means if they try a chargeback you can inform them that unless they close it within 24 hours you will take their details to the police.