What if my customers invoice/purchase was billed/delivered to a Dutch/European address? /

If your customers invoice was billed to a Dutch/European address, or if the purchase was delivered to a Dutch/European address, your customer can still get a VAT refund if the invoice has been stamped by customs. 

If there is a customs stamp on your customers tax-free form or on his invoice from your store, the export of the goods and your customers non-EU residency has been checked by customs and you are allowed by the tax administration to process his VAT refund request.

You can read more about the customs stamp and customs procedures to ensure your customer has exported the purchase here.