I found John at Busted Knuckle through Yelp reviews. I gave him a call in the evening, and he took the call although he was waiting in line for a table at a restaurant. I quickly let him know what I needed, he said he could be there the following morning, and asked me to text him the details.
The next morning, John showed up just before the time of the appointment, tested several systems, and came back with a diagnosis in a half an hour or so. I have followed up with him by phone a couple times for details since, and he's been an excellent communicator.
I'd gladly recommend John and Busted Knuckle, and will use him again if needed. Thanks John.