Sorry, but that doesn't look like any type of firearm to me. Even assuming it's early "17th century", by that time arquebusses and crossbows would be the more efficient (and common) weapons, and much easier to use.
Going by the stated dimensions (9", which would be close to actual size on my screen) the pole used to hold it would be rather thin, and not something you'd want to be holding due to the recoil when the "nine barrels" went off (not to mention that the whole thing would fly apart where the tubes are welded to the decorative part.) Also, there is a distinct lack of touchholes visible.
I wonder if the "Guaranteed authentic" part includes a refund, because I believe that whoever wins that auction is going to be rather disappointed at receiving (what I think it is) part of a cast iron lamp post....