Maybe he doesn't have a bank account and if not, he would have a problem trying to get a bank money order cashed. There is a lot of fraud involving bank money orders (I retired from banking and one of the areas I managed worked on this type of fraud).
Maybe you can cash a Postal Money order at the Post Office....don't know.
I did have one guy who only accepted Postal Money orders, no PayPal, checks, or bank money orders.