If you want a great selection of used watches in all of the major brands that come with a warranty you should visit the website for Gray and Sons. They are located in Surfside, FL one block away from the Bal Harbor shopping center.
They also have some new, still in the box with papers watches available. It is hit or miss on certain models and you have to be patient as they receive new inventory daily.
https://www.grayandsons.com/