I agree that a USPS money order is a pain in the butt. You cant get them cashed at a post office because they NEVER have enough cash so you have to deposit them and usually wait for them to clear before you get your money. My bank will do a cashier’s check for little or no fee and if a seller doesn't want that - then I will reconsider a purchase.
For me, a check edeposited is the quick and easiest.
