Moving to a 3BHK, but these hidden costs are a nightmare

Are builders just adding random charges at possession now? We're trying to upgrade to a 3BHK in Nai Basti Dundahera for the kids. Heard about crazy hidden costs like club fees, power backup, and a 'maintenance fund' that wasn't upfront. Gulshan Homz projects too? Also, the super area vs carpet area difference feels massive. How much can you actually challenge these surprise fees? What did you do?