Super area vs carpet area games are just daylight robbery.

My last site visit, Blessings Homz in PI Greater Noida, quoted ₹78 lakh for a 2BHK. But the super area vs carpet area difference was just insane, almost 35%! I work in real estate, but buying for myself, I'm still shocked how builders play these games. Is this normal practice now, ya sirf inka trick hai? They're pushing a construction-linked plan, asking for 15% upfront. As an investor, I'm thinking about leverage. Should I push for a lower upfront or a down payment plan for better negotiation on total cost? Kya lagta hai, which payment plan option gives more power to negotiate the final price? Off the record, any tips on getting better terms?