If you receive a Postal money order, don't ship your item until you have the PO verify the money order. We have been coming across a lot of fake PO money orders, usually associated with a Craigslist scam or an off ebay transaction.
https://www.usps.com/shop/accepting-money-orders.htm
This link will give you some tips on the fake money orders. They are pretty good fakes to the untrained eye, but the big tip off is usually the foil strip on the front.
Rick