If I sell a vehicle directly to someone, I will answer questions after the sale, as a common courtesy. Otherwise, the sale was "as is".
If I sell a vehicle to a dealer, after the paperwork is done, if contacted by the buyer the dealer sold the vehicle to, I'd probably tell them to speak to my attorney on their own dime or just pound sand.
I generally am not that rude, but I've had an acquaintance or two actually get asked questions (like how the vehicle was driven, how much traffic on roads, etc.) by the person whom the dealer sold the vehicle to, then a lawyer calls with a demand letter for how much the vehicle is "really" worth, and to pay the difference.
