as long as it was well understood that the price you offered was $800 and he agreed, then i say no, the deal was done. He's just trying to guilt you into giving him an extra $200.
No, deal was done
Yes, misunderstanding, your still getting a good deal
as long as it was well understood that the price you offered was $800 and he agreed, then i say no, the deal was done. He's just trying to guilt you into giving him an extra $200.