What can I do to resolve this problem?

I sold my 2003 Chevy blazer to my cousin. I sold it for 2000.00 because he needed a car for work. Well, my cousin had it for a year now. He says that he's having transmission problems, so he had it rebuilt. But he says that something is still wrong with it. He wants me to help him repair it. I said no. It was sold as is. I had no problems with it when I owned it. I do know that used vehicles present problems but come on. Before I sold it to him, I had it inspected and got new tires for it. Now he has his mother asking me to repair it. Now they are mad at me. In the past 5 years he has damaged 3 cars. Two of them he wrecked (he was in the wrong both times) and third car's motor was damaged. But this is my fault. What can I do to resolve this?