Said-Ul-Ajaib property: all-in cost confusion

Said-Ul-Ajaib – I've been checking out properties here for a few months now. Found a 2BHK with Kaanha Associates that looks promising, around ₹1.6 Cr. My parents keep saying to be careful about hidden costs, and honestly, I had no idea how much extra stuff adds up. Is the listed price ever the final price? Seriously, how much can you realistically negotiate off in Delhi? I'm seeing 1-2% mentioned, but is that even possible with builders like Kaanha? And what about stamp duty, registration, PLC, parking, interiors... do these add up to another 15-20%? I'm so confused about the true 'all-in' cost. What hidden charges should I watch out for right before possession? Ab samajh nahi aa raha.