Beyond the RERA number: How to spot builder red flags

My landlord just hiked the rent again in Mohali, so I'm finally taking the plunge and looking to buy my own place. I'm checking out some projects in New Chandigarh. Builder ka RERA registration kaise properly check karein? Matlab, beyond just the number, what are the actual red flags? Aur agar builder delay karta hai possession, toh RERA ke under kya real options hain? Does it actually help, ya bas paper pe hai?