Upgrading from 2BHK – worried about builder legalities

Visited Ansal Zinnia Garden last weekend, thinking of upgrading from my 2BHK. Builder ka track record check karna bahut important lag raha hai. How do you guys actually verify RERA registration properly? Matlab, red flags kya hain? Greenarc Homes ke legal issues bhi sune hain. RERA complaints kitni effective hoti hain agar builder default kare?