Something smells fishy. Who's to say the guy didn't swap out a board (your working CPU boards for his unworking CPU boards) while at home? This hobby isn't a stranger to slimeballs.
That said... maybe that's not the case at all with this guy.
But if he inspected the game before agreeing to pay you and take it home, then it's on him. He bought it as-is.
A more honest person wouldn't become belligerent right off the bat and would be civil when calling you back and asking you if you could help him.