I've been looking for a good argument all day, and I have to say this thread has left me a little underwhelmed, even after my reply below.
Relax a little why don't you?
Jesus H! I have to pay more attention to user names. I just realized that you weren't the person asking the original question, but were instead someone offering REALLY BAD ADVICE that will only get someone burned. I'll tear it down for you now.
ask if he can ship COD (cash on delivery).
Nobody in their right mind would ever ship COD for an eBay auction. This isn't 1950. You also absolutely cannot inspect the content of the package in any way before paying. Once you pay, those funds are GONE. PERIOD. This is not a safe way to handle a transaction for any party involved.
Any payment with money order other than in person with visual inspection of item before money changes hand is usually a scam.
It doesn't mean it's a scam and "usually" is a very broad brush. I'm willing to offer you this counter: There's a good chance there are more fraudulent money orders sent than fraudster sellers asking for money orders.
USPS money orders are traceable. You can send it with delivery confirmation and signature required.
You're confusing the features of a money order with the features of USPS's mail service. But yes, you can inquire as to wether a money order was cashed and where it was cashed and MAYBE by whom - but that's not guaranteed - it SHOULD be the person named on the money order of course.
If you get scammed you can file a claim with the USPS
That's not going to help you even if you can (and you can't necessarily). Especially if the money order, like most sold around the world, was purchased from a bank. Sending a money order is like sending cash with the benefit that you can confirm when it's been processed/cashed.
or cashiers check from your bank. Ask bank about buyer protection if you get ripped off.
Again, this is like sending cash with only proof of acceptance. Neither provides you with any security whatsoever. The only secure method of payment online is ESCROW. The next best thing is PayPal and Credit Card funding for auctions or straight-up credit card for businesses with their own merchant account.
Seriously, stop giving bad advice, you're going to get someone burned.