What should be checked when buying an oil burner ignition transformer online?

Check model compatibility with the burner, required secondary voltage rating, mounting footprint, primary voltage, duty cycle, and connector style. Verify the seller provides genuine part numbers, clear photos, and return policy. Inspect for certification markings, insulation condition, and packaging that protects against moisture and physical damage. Confirm wiring diagram availability and match it to your burner control scheme. Avoid unknown brands without data, and do not install if there are cracks, carbon tracks, or damaged high voltage leads because ignition systems operate at hazardous voltage levels.