RERA registration alone isn't enough for builder trust.

Spent the whole Sunday checking out options in Sector 85, including Goyal Luxury Floors. I'm currently in a 2BHK, thinking of upgrading. Builder ka RERA registration check karna kitna important hai? Matlab, agar builder ka track record theek nahi bhi hai, toh bhi risk hai na? How do you guys verify a builder's legal history beyond just RERA? Any red flags?