Hidden costs buyers only discover after possession

Budget finalised, loan pre-approved — now stuck. Strategic Developers in Sector 22 Yamuna Expressway looks good, but their 'all-inclusive' price feels fishy. I'm worried about hidden charges at possession. As someone in real estate, I know they add PLC, OC, IFMS later. What's the real negotiation room on a ₹90L 3BHK? Anyone faced this?