Did you sign a Bill of Sale?
When I sold my pickup truck, I had the buyer sign a Bill of Sale or release of Liability Form, so I don't have any responsiblities afterwards. Like others said it's "as is" sale. So if he doesn't check the condition of your car before he decided to buy, it's his fault. You don't need to pay attention to his words. Also Google your questions, I'm pretty sure you will find useful answers on the internet; they will be more helpful than people here.