Possession ke time itne extra charges kyun hote hain?

Mai abhi Salarpuria Sattva ke Uppal project mein shift hua last month. Builder ne bola tha no negotiation, par registration aur PLC ke alawa bhi kaafi hidden costs the. Maintenance advance, utility setup, society formation fees... yeh sab surprise tha. Sabko aise unexpected charges mile hain kya? Kaise avoid karein next time?