If it is still a good deal at $1,000 then do it that way. Then both parties are satisfied with the transaction. ALWAYS write up and sign a bill of sale to avoid confusion. I may have interpreted that "$800 cash today" meant just that, 800 now 200 later. Another idea would be to split it and give him $100 and tell him that since it was a misunderstanding that you would be generous and go half of the difference. You were just as surprised that he wanted another $200 as he was that you weren't giving him another $200. Compromise is where it's at.