Passive income starts with active underwriting. Before I get comfortable with a rental’s base case, I run three quick tests: 1. Rent down 5% and vacancy up to 8% 2. Operating expenses up 10%, with management, turnover, and capital reserves included 3. Refinance delayed or unavailable at loan maturity I look at the combined downside too—not just one variable at a time. If a small miss wipes out cash flow or pushes DSCR too close to 1.0, the deal likely needs a lower price, better terms, or more reserves. Which assumption changes your deals the most: rent, expenses, financing, or exit value?