1. Always write "Do Not Forward" by the sender's and addressee's addresses.
2. To verify contents, make a video recording whenever a package is opened or sealed. If you still lose a credit card (or other) dispute despite showing them the recording, submit the video to the recipient's county detectives and pursue criminal charges (you could also file a lawsuit if reasonably local).
3. Use extremely safe Registered Mail whenever possible. Always use a very large box to greatly speed up transit time (post offices hate having space-hogs in their safes).
4. Always pay extra for Signature Confirmation, even for Registered Mail, whose included signature is strictly internal and will not be accepted by online platforms.
5. Use a box in a box with lots of filler paper or other material.
6. Use fiberglass-reinforced packing tape. And lots of it, sealing every crack and opening.
INSERT OTHER TIPS BELOW!