Negotiating PLC charges: something builders won't tell you

Visited a Neoshape Infratech project in Sector 9 last week. Honestly, I had no idea about PLC (Preferential Location Charges). The sales guy acted like it was non-negotiable, but my uncle, who's been investing for years, told me to push back HARD. Apparently, you can often get a discount of 20-30% on PLC if you're persistent. He said builders inflate it knowing most first-timers won't haggle. Also, he mentioned checking the RERA registration CAREFULLY, especially the completion date. Delays are super common. Is it worth investing in under-construction property still, given all the risks? My parents keep saying ready-to-move is safer. What are your thoughts? Is there any truth to what my uncle said? Hope this helps someone.