Broker tactics on stamp duty are shady

Visited a couple of projects in Sector 70A last weekend, including one by VK And Sons. I'm currently in a 2BHK, thinking of upgrading to a 3BHK, maybe around 2.5 Cr. Builder ka price toh ek cheez hai, but what about the actual *all-in cost*? I'm talking stamp duty, registration, legal fees — brokers don't always explain these clearly. Is there any way to negotiate these or are they fixed? Also, do brokers give a better deal than direct from builder on these charges? Already have a home loan, so trying to budget properly.