Janos,
You said the Moon, Saturn and Jupiter were fantastic
So a mark on the mirror, maybe not that big a deal!
If it had holes in the coatings as Geoff has said, ring the dealer back. If its just a spot of dirt or something and not very big don't be to concerned. Chips on the edge of the mirror won't affect things to much.
If your happy with the views and by the way you sound you are.
Just get out and enjoy the night sky.
Best.
