Circle rate higher then market rate of old flat

I think it has been increased to 10%. Further if the circle value is inflated, we can proceed with the actual receipt and challenge the valuation later in if scrutiny falls

Yes as per the new rule circles rate and sale rate different will be 5% then allowable
if not then capital gain calculation will be done taking circular rate not as per sold rate
and The buyer has to pay stamp duty on registration value which cannot be lower buyers the circle rate besides that buyer also pay tax on the difference of amount that is circle rate minus market rate under section 56(2) of income tax act as it considers as a profile to a buyer profit
as per the budget of 2018

Circle rate will prevail and tax calculated accordingly for buyer and seller. This year I think from a buffer rate of 5% , it is 10% in view of Covid.