Noida Ext. 'fixed price' policy is just a starting point.

Is that 'no negotiation' policy from builders in Noida Extension really true? I'm currently in a 2BHK in Sector 45, thinking of upgrading to a 3BHK or a small villa near Yamuna Expressway, maybe from Gaurs or Essential Homes. Already have a home loan. Builders like to say 'fixed price', but kya sach mein koi room nahi hota? I'm an investor, so maximizing deal value is key. Heard about some 'spot discounts' on the last few units. Is that just a marketing gimmick, or can you actually get a solid percentage off the quoted price? Aur hidden charges ka kya scene hai? Possession ke time pe kuch unexpected cost toh nahi aate? Any tips on how to push for a better deal without sounding desperate?