Calling to verify is slightly better than useless. The other party can still report it lost or stolen and you just end up with a nicely colored piece of useless paper.
If you get the MO in the mail, before shipping your goods, you go the PO and they either give you cash on the spot or tell you it is fake. You can then make your decision to ship, and ship it while you are at the PO if you choose that means.
Even if your bank cashes it, if it is fraudulent, the cash comes out of your account. It can take weeks to clear. If you ship your goods, you are fooked. Emphasis added for those who aren't 'getting' the concept.
I received a MO that had a name scratched out and mine was written on it. Correction initialed by the buyer, too. Guess what? Altered MO are not accepted by the PO, good or not. Even though it was an honest mistake, this is a good FYI, because I am sure this could be used as a scam in some way or another.......
Our local contract PO stations aren't cashing USPS MO anymore, because of the high volume of fakes that are flying around. Cash it at a PO, not a bank.