@Herbeca,
An official art appraiser should be the only option for you to consider.
No one here knows what country you live in. This is an international forum with active members from Canada, the US, Australia, and beyond.
No one here is a professional or even amateur art appraiser.
Quote:I found out the violin from the estate that went to my father’s cousin turned out to be a Guanaeri, valued over $10M.
You claim this. Taken at face value that you're not just lying. One can assume the art you are asking about is valuable in its own right. A professional appraiser would also consider advising you on how to restore the artwork by an experienced art restorer.
Wasting your time here? Well, is a waste of time. If you don't trust Google and its results for a professional art appraiser? Go to a high-end art auction house to see if they have an inhouse appraiser or they can refer you to one or a related firm to get what you feel needs to be done.