Bengaluru payment plans: What they don't tell you

Did a site visit to 42 Estates project near Panathur last weekend. They're heavily promoting construction-linked payment plans. From an investment perspective, I'm trying to gauge if offering a larger upfront down payment could unlock better pricing or more favourable terms. Also, the super area vs carpet area difference felt significant there. How do you guys verify actual usable space before committing? Is it common to negotiate based on carpet area rather than super area? What's the community's take on leveraging payment plans for better ROI?