+1 to user-removed. This is a common scam involving shipping items overseas. He sends you a cheque for more than the combined value of the car plus shipping costs. You bank the cheque, which clears, then arrange for the car to be consigned to Mumbai, and send a cheque from your account to his sister.
Then, due to some arcane mechanism within the bank clearing system, his cheque (which had cleared) bounces, leaving you out of pocket for the sum that you sent to his sister, plus you haven’t got a car any more.
It’s a scam. Save yourself any further mental energy and ignore any subsequent emails.
Good luck finding a genuine buyer for your car.