Legal checks nobody talks about enough

Did a site visit to Emaar Emerald Floors Premier last week, really liked it. My friend just moved into a flat on Dwarka Expressway and is already facing issues with his OC and title clarity. It's making me super paranoid about legal due diligence. Honestly, is checking the encumbrance certificate *before* signing anything really that crucial? And how do you even verify a builder's past legal track record, like Gurugram Land and Finance, without getting lost in paperwork? What hidden legal red flags did you all find?