When sourcing used machinery, the mechanical condition and output precision are paramount. You must verify the motor brand and power rating (preferring Siemens or Delta for longevity), the production speed (e.g., stitches per minute for quilting machines), and the maximum mattress thickness the machine can handle. For tape edge machines, check the arm stability and sewing head brand (e.g., Singer or Pegasus). Always request a video of the machine in operation to check for abnormal noise or vibration.