The situation with international shipping from a U.S. Post Office (USPS) has got pretty difficult, even dire. Not everyone outside the U.S. is aware of this, so I offer an explanation of the facts.
First, we in the U.S. consider ground shipping ("Parcel" rate) unacceptable even for shipments among ourselves, that is, within the country. A cursory review of eBay postings will confirm this, if you need such confirmation. Thus, air rate ("Priority Mail") is the new Parcel. It has in fact replaced the bottom rate of our parents' day. It is the new normal. Ground rate is considered unreliable and excruciatingly slow, though it is mainly the unreliability that is the issue.
Second, there is as of right now no way to economically guarantee a USPS shipment outide the U.S. USPS does not track Priority Mail International, thus it cannot be guaranteed. And since USPS won't, I can't either. There is a higher level of Priority Mail International that is trackable, called Priority Mail Express International, but it is so expensive as to be on a par with international services from UPS, FedEx and DHL. For my customers, I send proof of mailing in the form of copies of the shipping label showing the purchase of the shipping. This is all I can do for international shipments.
Speaking of DHL, the gold standard in international shipping, it is a viably reliable way to ship anywhere, even to the far east and Latin America. But incredibly expensive.
Finally, I cannot falsify customs documents, so please don't ask. For all international shipments I declare on the customs forms the correct value, but I will also write "Used motorcycle parts for repair." For most countries' customs departments, this is effective in lowering your customs duties. Thank you for your understanding.