Best farriers I've had are the two I have now. One because she was so great at helping with my horses transition from shod to unshod (my horses as always been purchased younger and never shod). She was great helping get my mare through the transition. She's no local, but knew the stable owner and was glad to make a trip each month to get things right with my mare.
Then came the long haul of getting her feet toughened, but for me it's worth the timeis takes, so that I can ultimately ride on any terrain.
The other guy is local and very patient. Not a problem with my girls, but he is very patient with horses that don't like their feet worked on. For mine does a lovely job of leaving them a level natural foot complete with the roll (not they call it a Mustang roll, but we didn't have a fancy name for it 40 years ago when I started having horses).
In the end I guess a good farrier is one that gives you what you want and keeps your horses feet always healthy. No horse I've owned has ever had so much as a sore foot no matter where we rode, so I can't complain about any of my trimmers.
So I guess that what to look for. A healthy, happy horse, with never a foot problem no matter what you want to do with them.