Ghaziabad property: The true art of negotiation and avoiding hidden fees

Negotiating 5-7% off on a Ghaziabad property often gets dismissed, but I've found it's possible. For a 2BHK in Shastri Nagar, targeting ₹70L, what realistic percentage have others managed to shave off? Beyond the base price, the all-in cost with stamp duty and PLC can add 10-12% easily. What hidden charges from builders like Paradise Homes should one specifically watch for at possession to avoid nasty surprises?