Paypal puts the seller at a disadvantage because the buyer can claim damaged goods, but at least has to return it. Sending a MO puts the buyer at a disadvantage because the seller can just pocket the money.

And, by the way, even USPS MOs can be forged. Mail fraud? Yes, but I suspect they have bigger fish to fry.

If a non-local seller insists on a MO today, I move on unless I'm desperate.