This is one reason I never ever use money orders anymore, unless its someone I know from this forum who can be vouched for.
I have gotten bruned twice. Once I got my money back (over $500) but it took forever and a lot of leg work on my part thru the USPS process.
Maybe the guy has fallen on some health issues or something...always like to think that people are basically good...but who knows.
If you have a legit address you could visit or send someone to visit...call the local police maybe they can at least verify the address isnt a front for something. ?