Gurgaon builders hide 20% of the real cost, prove me wrong.

Since January I've been shortlisting flats, especially around Sector 84. I work in real estate but buying for myself is different. Ashiana Housing mein they quoted X, but all-in cost mein kitna upar jaata hai from quoted price? Possession ke time kya naye charges aate hain jo discuss nahi hote? Aur spot discount milta bhi hai ya bas marketing gimmick hai? Kya lagta hai?