Bottom line is that you either post with sufficient tracking to satisfy Paypal or you refund, ebay cannot police this and unless you have fully tracked proof of delivery to their address there is nothing the police can do either. If they are silly enough to try and say that fully tracked parcels have not been received and enough sellers can band together then it is possible to get them stopped. Some of you will remember a certain seller who ended up frantically trying to return goods and make payments after she was reported to the police and had a web page dedicated to her misdeeds.