Gurgaon builders' 'final price' is never final.

My all-in cost for a 2BHK in Sector 61 shot up nearly 15% from initial quotes. I'm looking at another property now, maybe a 3BHK on Dwarka Expressway, and trying to learn from my first experience. Does price negotiation even work in Gurgaon? Builders like Krrish Group seem pretty firm. How much can you realistically knock off the base price? And what about all the hidden charges like PLC, OC, maintenance advances? I got hit with a bunch post-possession. Should I expect these to always be a surprise? Any tips for an investor trying to maximise deal value?