Basically what everyone else was saying, but before they go to the spot, the killer would drop the 10k, then Jojo would walkover to where it was dropped before it showed up and pretend to drop the ammount of money that he showed in the trade to the victim.
Then the 10k would show up and they would think it was what Jojo showed them.
Well that's how i used to do it as well, i think Jojo had much better "Chat-up lines" than any other lurer did though.