Sorry to hear about your loss. I live outside the USA and have discovered it is a risk using the different national postal mailing systems. Norwegian mail, for example, has no clue what an American "registered letter" means. The private systems are more secure, but so much more expensive!
I agree with the Paypal system for payment. When someone wants a check payment, it isn't always workable to do so (affordable way) between countries. Paypal account is so easy to set up and transfer payment or money that I can't understand why more people don't do it.
I doubt you will ever see your money come back to you and that's a shame, but I do thank you for the "heads-up" and sharing your experience.