This is a case from a customer who purchased their oven in 2017. The oven they own is the Pizzaioli Brick Wood Fired Pizza Oven. This model is a traditional brick oven that has a stainless steel chimney flue system and an iron door.
The GREAT news is that it's relatively easy to clean. You can scrub the rust off with a good bristle-wire brush and, afterward, we also recommend that you coat the door and chimney flue with a high heat Rustoleum paint to prevent further rusting and to give it a more fresh look.
You also want to ensure to keep the oven covered during inclement weather and when the oven isn't being used for extended periods of time.
Here's another example from a different customer with the same concern.