When buying a used spin bike, it is important to consider the condition of the frame and components. Look for signs of wear and tear such as rust or corrosion on metal parts, frayed cables, worn out pedals, brakes that don•t work properly or squeaky chains. Additionally, inspect the flywheel for any damage or imbalance which could affect performance. Check if all bolts are tightened securely and make sure there are no loose parts that can cause an accident during use. Lastly, test ride the bike to ensure it is comfortable and in good working order before making your purchase.