Here is my experience how I found a watchmaker. I am not sure if this is to be replicated, but it is worth a trial:
I had a watch that was not working anymore, and I walked into the local Omega boutique, asking if they have a repair service. The person I talked to asked to see the watch, and a brief conversation about watches and repair ensued. Then, he took out his cell phone and started dialing, and asked his contacts if they would accept my particular watch for a repair. I left with two addresses and phone numbers. This was a very good experience.
General recommendation: Go to places where a lot of watches are handled and who do not have a self-interest to get your business, and listen. I have found that watch people help one another.
But the question was about a good watchmaker. A recommendation from a person who deals with a lot of watches (the person in the Omega boutique) is a good start. The missing piece can only gained by experience. I look for a clean workshop with good lighting, and a dedicated person that repairs the watches. I personally do not care if there is a certificate from the great grand watchmaking school of Val de Cordon-Bleu (or any other meal) on the wall. I judge by timely repair, not necessarily fast, but do they stick to the promised deadline. I judge by communication. And I judge how the bill looks like. Itemized? List of parts replaced? Time grapher details? Warranty on the repair?
This is a bit like finding a dentist. Eventually you got to do it, and everybody claims to have a good one.
Good luck