address letter to RTo by regd post AD informing them of sale of your car .
2) enclose copy of delivery note received by you and proof of payments received by you .
3) also send letter to local police station that purchaser has not transferred car in his name yet and you apprehend car may be used for terrorist activities .
4) you can also publish public notice in 2 local newspapers that the seller shall in no way whatsoever be responsible for any misdeeds,unlawful activities or any acts of omission or commission with the motor vehicle (state make, model,type of body,registration number, engine and chassis nos.)by the buyer or any other person who directly or indirectly uses the motor vehicle for such misdeeds,unlawful activities or any acts of omission or commission. The liability of such misdeeds,unlawful activities or any acts of omission or commission shall solely rest with the buyer of the motor vehicle."