The super area trick nobody talks about in Greater Noida

Since last Diwali, I've been looking at 2BHKs around Yamuna Expressway, budget ₹70-80L. Builders like Rajesh Projects show great super area numbers, but carpet area mein kitna difference hota hai? My broker says it's normal, but I'm worried about paying for 'hawa'. Also, stamp duty aur registration ka final bill kitna ban jaata hai? Is there any way to negotiate that part, ya fixed hi hota hai? Kya kisi ko real world figures pata hain for Gunpura properties?