"Mystery items", in the sense of "I'm putting a coin in a brown paper bag so you can't see it - bid on it and you never know what you might get!" are prohibited on
ebay. I know this is different to selling a "mystery coin" in the sense of "I don't know what this coin is or where it came from but I'm showing you clear pictures of it so maybe you know what it is", but something may have gotten lost in translation on the German end.
One final thing... if you know it's an Iraq 10 fils 1933, what's "mysterious" about it? Why not just describe it as "Iraq 10 fils 1933" rather than "mystery coin"?

Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis