You can ask him to procure a certified copy of the registration document by first making a police complaint, obtaining a non-traceable certificate from police, and then publishing the same in a newspaper as a public notice, wait for 15 days for any objection from any quarters;
After that you can ask the vendor to execute an indemnity bond indemnifying the loss or to pay or compensate for the losses, damages or liabilities incurred by the buyer in this connection at a later date
After obtaining all these formalities, you may get a legal opinion in this regard and then proceed only if recommended to buy.