Negotiation secrets builders don't want you to know

My last deal, I managed 4% off the listed price. Ab Greater Noida mein, especially Royal Next Homes jaise projects par, kitna negotiation expect karein? I'm eyeing a 2BHK in Sector 18, around ₹85 lakh. Kya secondary market mein resale properties par zyada room hota hai for negotiation compared to new builder inventory? Also, possession ke time jo hidden charges aate hain, like extra PLC ya utility connection fees, unko kaise avoid karein ya pehle se account karein? Is 5-7% off too optimistic?