Soo ... update from me: The first used X I received did have a swollen battery and a lot of scratches even though it was supposed to be mint, so I sent it back. Bought a refurbished "like new" one from a dealer for a little more money, and that one actually is like new: Not a single scratch, 100% battery health and Apple warranty until July 2020. I'd say that was a good deal.
Nice. Congrats. Enjoy your phone. Yeah never buy refurbished ones from third-party, only directly from Apple. They are basically brand new ones. Well i don't know where you live, Apple's own clearance sale is only available in the US.