In an effort to keep postage affordable, I use a courier. They do not deliver to PO boxes.  All my listings have a note under the "Terms and Conditions" stating that if you have a PO box, please contact me before bidding so I can estimate using AusPost.  So of course, I get a buyer who immediately pays using PayPal without waiting for invoice, and has a PO Box. It will cost me $4 more to send via AusPost satchel (on an $8 item.  Have requested buyer send me a street address, but what do I do if not?  She can claim she paid amount owing via PayPal and therefore shouldnt have to pay more, all because she didn't read the whole listing.