Legal clarity for 3BHK upgrade, need advice

Budget finalised, loan pre-approved – now stuck on legal clarity for a 3BHK upgrade in Greater Noida. I'm currently in a 2BHK but looking at options around Noida Extension, maybe even ATS Knightsbridge. Heard scary stories about title verification issues and RERA compliance. How effective are RERA complaints, really? What red flags should I look for checking RERA registration for builders like Vrinda Group? Don't want legal hassles; already have one home loan. Any real-world advice on due diligence before putting down money?