xiaobaitu and experts, please help. car sale dispute affect GC?

If was accused "intentionally cheating" while selling a car privately(though I didn't), would it affect the GC application?

Sold an used car ($2200) to an indian guy last week, timing belt broken while he drove the car to home. Called me second day claiming will take it to court accusing "intentionally cheating" if I don't give hime another $300. I'm worried that even if I give him $300, he can come again saying other things are wrong. (Radiator leaks while I got it)

Really need help and advise, thanks a lot.