Apple has started selling certified refurbished Apple Watch Series 9 models in the U.S.The refurbished Series 9 models are approximately 15% cheaper than brand new models, with prices starting at $339.Apple ensures its refurbished products go through a thorough cleaning process, inspection, and full functionality testing.It is expected that the Blood Oxygen app is deactivated on refurbished Series 9 models due to a legal battle with Masimo.