Here are the important factors for buying a resale flat: 1. Age of the flat, 2. Existing mortgage, 3. Facilities and amenities, 4. Expenses of repair and renovation, 5. Property valuation, 6. Brokerage. And the list of the documents that you need to check before purchasing a resale flat: Title Report, NOC from the Bank, Building Approval Certificate, Occupancy Certificate, Encumbrance Certificate, Utility Bills, Latest Tax Paid Receipts, NOC, etc.