Lawey notice for professional fees

Dear Sirs, 

I choiced an apartment 2 bhk. Its a resell flat and full vacant flat and I will buy in full cash.
Donot buy the property only in hard cash,make payment in chq. as u will have proof that u had pay the amt for the property
Now while negotiating I found out that the seller will only sign during registry after getting full payment of the property by hard cash.

why he is insisting on hard cash .it is risky , later he can denay that cash has not been recd by him as u donnot have any proof of payment.

Now is it safe ? I mean to say give him the full amount in cash, and then if he denies to sign the selling deed then ? 

it is not safe to deal in property only in hard cash.

What provisions are available in law in this type of transaction. 

Please advice as soon as possible.