Thanks to all of you for your replies. I have taken your rewording suggestions on board and am about to change some of my current listings to the new wording. Will also investigate the option of of excluding PO boxes. 

However, if buyer had read the postage options, she would have clearly seen that this listing used a courier. She has not yet replied to my emails, so presume she will just ignore request to provide a street address.  Sigh!