Delhi negotiation is mostly a myth

Been looking at flats in Karkardooma for 6 months now. I'm in real estate, but buying for myself is a different ballgame. Builders ki marketing ka pata hai, but true costs always seem to inflate. Shri Shyam Realty ke ek project mein 2BHK dekh raha hoon, around ₹1.2Cr. Ismein kitna negotiation possible hai? Log kehte hain 5-7% easily ho jaata hai, but I'm not sure. And all-in costs ka kya scene hai? Stamp duty, registration, PLC ke alawa, what hidden charges typically pop up during possession? Want to avoid surprises.