Income tax implications

Sir,

I am purchasing an office, commercial property in Mumbai. The seller is member of the Registered Society. There are unauthorized tenants inside the premises and the seller got around 150 sq.ft in his possession. The seller is selling this 150 sq.ft as is where is basis. My doubt to be clarified is -

 

a) Whether I need to pay stamp duty for the entire area of 500 Sq.ft or only for 150 sq.ft?

 

b) The seller is taking 25 lakhs, however the Market Value as per Ready Reckoner is 150 lakhs. If, Stamp duty will be paid on 150 lakhs, what's the Income Tax Implications to both the buyer as well as the seller?

 

Thanks in advance.