Once deal is confirmed, then first token money is given like 20K, 30K, 50K, etc. with an agreement that balance payment will be given in a 2 days, 3 days or a week time etc..
You need to arrange a sales-purchase deed on stamp paper with 2 witnesses.
Receive the money, give them car & its smart card.
May I know which car you want to put up for sale ?
P.S. if mode of payment is Cross cheque, P.O., Bank Draft, etc, then first let the payment credit to your account which normally takes 24-36 hours.