I have encountered several problems with PayPal when shipping items overseas since tracking numbers are not available when shipping via USPS. Unfortunately several of my buyers claimed that items were not received. Since I had no tracking info, I lost my payments through the automatic action taken by PayPal.
It is always possible that your buyer is using fraud to receive a so-called free article and, I am sure, this does happen. I therefore suggest that you check his or her feedback profile which can be obtained fro eBay. It is also possible to set your sales page so that only people with a certain feedback score can bid on or buy your article. I suggest that you set your cut-off point in relation to the price of the article. We often sell watches which range in price from $ 200 to $ 300 and we set our cut-off feedback score at at least one hundred.
I also urge you to buy insurance for all international sales and shipments. You can obtain this at a reasonable cost from Auctiva which I use to list my items on eBay. Their rates are $ 1.65 for items under $ 50 with a sliding scale up for more expensive items. The cost of insurance is paid by the buyer.
You can obtain a Certificate of Mailing from USPS for $ 1.05 and this seems to be acceptable as proof. I discussed this by phone with PayPal but am not certain that it will be accepted when the problem occurs since PayPal usually sides with the buyer. They prefer that you use UPS since they issue tracking info. However, the shipping cost via UPS is much higher than USPS.