Ghaziabad investors: What's the real negotiation limit?

Rasulpur Sikroda mein Ishaan Group ke projects par nazar hai. I work in real estate, but for my own investment, it feels different yaar. Builder sales reps always say fixed price, but Ghaziabad mein price negotiation kitna possible hai? Matlab, realistically, kitna % off mil sakta hai? Aur all-in cost mein kya hidden charges hote hain jo sirf possession pe reveal hote hain? PLC, parking ke alawa aur kya add hota hai? Trying to get the total acquisition cost right. Any actual buyer experiences?