It does look spot on like the coat of arms of the German Confederation, which came to be after the Napoleonic Wars, a bit later than 1775. That doesn't mean that this couldn't be from 1775 though. The Eagle symbol was used by many family's and cities in Germany as part of their coat of arms, not to mention the Emperors. I might hypothesize that this particular rendering may have came about just as a general depiction of the eagle for the German people. It lacks the more specific coat of arms elements of some of the others I've seen from that time, the ones that represent the Aristocratic family's etc. This design may then have been chosen (later on) by the German Confederation. That makes since to me. A sort of vague Eagle coat of arms that represents everybody (in the style of a true confederation). In truth, Germany had long been a confederation, many states very loosely ruled over by the Holy Roman Emperors, particularly since the end of the Thirty years war in the 1600's.
Anyway, I think it's a nice piece. I wouldn't doubt that I low balled it at $125. I guess I don't really know squat about the value of something like this, authentic, reproduction, or otherwise.