Old 19th and 20th C German bows is a subject of interest and research and discussion of a fair number of people. Apart from those already mentioned, I would consider amongst others Josef Gabriel’s opinion certainly worth having. I hope he’s not cross with me mentioning him here.
The problem with “expertize” is that it is a lot more difficult than people think. If I am convinced that an anonymous violin is by Caspar Strnad, for instance, my conviction is based on me knowing at least 20 of his with an original label. With old German bows, the situation is much more complicated, due to the i