My 2BHK upgrade dilemma: Rajkot negotiation tactics

Krishna Kunj keeps coming up every time I shortlist something for my 3BHK upgrade. I'm currently in a 2BHK near Kalawad Road, looking to jump to a bigger space, maybe a villa or a large 3BHK around 150 Feet Ring Road. My budget's around ₹80L-₹1.1Cr. I'm weighing resale properties against new launches from builders like Balaji Group or Madhav Group. My main question is about negotiation. For a property like Ansal API's projects or something similar, can you actually knock off a decent amount in the secondary market compared to a new flat? Builders usually have fixed prices, but I've heard resale has more wiggle room. What's a realistic percentage to aim for, say, on a ₹90L property? And what about hidden charges? Any advice on spotting underpriced assets in this Rajkot market?