Regarding the car sales issue

I have sold my car to a local guy four days ago. Before I sold the car to him, I let him have inspection and check the car. I've show him everything of the car and the service history. He check everything and give me an offer. We finish the deal two days ago. He pay me the total amount in cash and I sign the ownership transfer form. I've also drop off my part to service SA yesterday afternoon.

This morning he message me and said that the car have some problem and ask me to either pay him money($1500) to fix or buy back the car. I was wondering in this situation, 1. With offer and acceptance. 2. Full amount has been paid in cash (consideration appear here) 3. All document has been sign two days ago and I don't know what he have done to the car engine this two days 4. I've let him inspect the car and show him every thing he need

So, I wondering can anyone give me some advice that whether I have the obligation to pay him extra? If there is offer, acceptance and consideration, is that mean a legal contract done and I don't need to respond to his request at all?

Thanks guys for helping :)))

交易完成的一瞬间就代表了你的责任的终止，后面出现的任何问题你都可以不用负责任，并且之前的问题你不知道也不可能全部告诉他，所以不用有任何反应。

there is no warranty for privately sold car. they have no right to ask for a refund or anything else. if they come to your place just call the police. you don't have to worry about it.

tell him fxxx off