Super bulit up issues ??

Dear Lawyers, I would like to clarify on certain things regarding a purchase of a flat in kolkata. My concerns are mainly with super built up and carpet area , i was recently quoted a price for a 4bhk flat which is 2900sq ft. @ Rs 9000psf., upon viewing the apartment i discovered that the carpet area is 1988sq ft, deduction are approx 30%.(why 30%) Now after a lot of discussion with appointed realtor/agents from the developers, Saying that "fine, we'll quote you the price for carpet area which is 1988sq ft @Rs 13000psf, (BIG WHY, STUNNED). now this is something new to me as i have lived abroad and have some experience in real estate industry, Why do these realtors are practicing such activities, and why is it still acceptable in this society? Apart hearing from some rumors that government has implemented new regulations such as the developers are not suppose to charge on basis of SBU or BU. but yet the pricing is than different than the market price on carpet area. is there anywhere i can find out the formal valuations for such market rates. is there any advise i can seek from this website. Thanks