It is always advisable to comply with the applicable provisions of Laws of the Land.
In order to have smooth sailing, you are advised to go for Registered Transaction before concerned Registrar.
It will not only give you upper hand but also it stands the test of laws.
Further more, the Registration charges etc., will be adjusted at the time of final transaction.
Do not ignore Bank, make it a party to the transaction.
Never pay the money to the seller directly, it should & must be routed through Bank only under proper acknowledgement.