Postal Money orders are as insecure as Western Union. The Post Office does not care about the business transaction. So they will not get involved with the reason why you sent the money order. Cashiers checks are just as bad even though you can stop payment it is still costly.
The only way that you can 100% protect yourself from a transaction going south is to use PAYPAL or XOOM or similar transaction facilitator AND use a credit card. Preferably one that is NOT associated with PAYPAL. PAYPAL has become internationally accepted and you can use your own credit card.
Offer to pay the PAYPAL fees which are about 3%, that is a small price to pay for security. If the seller refuses to accept those terms then don't do business. The point of doing business is to transfer money. The seller controls how the goods are presented and delivered, the buyer controls how funds are transfered.
If the transaction goes south by either faulty goods, damaged goods, or failure to deliver then the credit company will ALWAYS refund your money. Of course you have to show them WHY the refund is warranted but a few photographs and documentation is all that is needed. And of course you have to return the goods. But document it well AT THE POST OFFICE, because the Post Office IS an authority and has federal investigative and law enforcement ability. Fedex, UPS or DHL won't be bothered. And insure it going back. The Post Office is also very good at what they do.
NEVER TRANSFER CASH. THAT INCLUDES POSTAL MONEY ORDERS, BANK TRANSFERS, PERSONAL CHECK OR CERTIFIED CHECK.
Better yet close the deal in person and save yourself the shipping and insecurity. If the seller INSISTS on Western Union or USPO money order and refuses anything else then walk away AS chances are there WILL be problem. To all those who fall into this category I can only say this: It is the 21st century get with the program. If you feel the need to "hide" transactions from the IRS or otherwise keep your transaction "off the grid" then that is your problem not mine.
And ALWAYS insure the package and if it is damaged OPEN it in the presence of the delivery agent.