What is registration value for a property

The circle rate of the property on the completion certificate that I am looking to buy comes out to around 68 lacs, however is it possible for me to do the registry for 65 lacs as the seller is insisting to save on capital gains tax. I being the buyer am willing to pay the entire stamp duty fee which would be levied on 68 lacs. Also, if that is allowed, will there be any legal consequences later for either the seller or buyer? Anything else that one should be aware of?