I had to use that once when a guy was trying to get me to pay for a 440 that I was supposed to pick up and he didn't have it pulled yet... He claimed to be "Waiting for his guy to pull it..."
I said that I would pay him when it was pulled and I was picking it up...
He wanted me to pay cash up front when I showed up to pick up the two engines that I was supposed to get from him, luckily one was pulled and I paid for and picked up that one... I told him that I'm just trying to keep a fool and his money from getting parted and if I had to pay up front I would send him a money order in the mail when I got home, that way if he didn't come through I could press federal charges against him... He shut up and stopped pressing me for the money after that...
I'm still waiting for him to call me to pick up the engine, and it's been over 8 years now.... (I doubt that he still has it....)
However I do have the money that he wanted me to pay for it....