Here in Canada, a U. S. international money order can be obtained at any bank, which makes it simple, also the bank will sell me sterling money orders. I have sent cash registered (tracked with a signature at the end) and it seems to be OK.
I do a lot of buying on EBay but refuse to deal with those that ask for paypal only payment. My bank, when I checked some time ago, refused to deal with Paypal, but a daughter tells me it is OK now.

I have received notice from a couple of California dealers saying that their banks charge for US international money orders, but I don't believe them. Of course Postal money orders are a no-no where the US-Canada border must be crossed. Banks can't accept them.

Probably none of this will help.