The discolored medallion would be the least of my worries.
The movement does at least have the wrong rotor - or it’s just a transplant of a non-chronometer 501 into this Constellation. There shouldn’t be a sunburst dial in a 2852, and on top of that, the seller is well aware of that and chose not to disclose any of this in the Riccardo offering. The watch was offered on IG for 1000€ or so, when the issues were discussed in the comments he participated at first, then deleted the post. I’d be hoping for more transparent behavior, especially from someone with 14k followers - this is just plain dodgy in my book.