When evaluating a used rebar bending machine, you must prioritize the maximum bending diameter (e.g., 6mm to 40mm) and the motor power (typically 3kW to 4kW for standard industrial use). Check the working disk speed; a variable speed motor offers better control for complex shapes. Ensure the internal gears are made of high-strength forged steel rather than cast iron to prevent premature failure under load. Additionally, verify the bending angle range, which should ideally be adjustable between 0° and 180°.