My 2BHK upgrade journey: Noida's hidden costs?

Visited AMR Infrastructures' project near Bhangel last weekend, looking at 3BHK options. Currently in a 2BHK in Sector 78, thinking of upgrading. Builder ne price quote kiya, but I'm wondering, Noida mein negotiation kitna chalta hai? Like, realistically, kitna discount expect kar sakte hain? I've heard about super area vs carpet area traps, and how builders inflate numbers. Is there any way to check this properly before finalising? Don't want to pay for space that isn't really there. Also, what hidden charges should I watch out for that only show up at possession? Already have a home loan, so trying to budget properly. Koi experience share kar sakta hai, especially with builders around FNG Expressway projects? Is it even worth trying to negotiate hard on new properties or secondary market is better?