I lucked out on my current room--the company was both residential and commercial and I tapped the commercial guys when I explained I wanted to install a 10kVA iso transformer as part of the package. These guys were used to doing all kinds of stuff, from auditoria and sports arenas to other big commercial projects. Their work was impeccable. Unfortunately the commercial group splintered off shortly after my work was done (no, I was not the cause) but I found another top tier electrician who did work on our kitchen reno and when I mapped what I wanted to do with a bypass for a Generac, he totally got it-- sort of the Fremer problem (though nobody else I know with a system and Generac has had problems).
Anyway, it is luck of the draw. I've had some terrible vendors over the years as well. My absolute favorite guy was not a licensed electrician- so I could not have him do any electrical work but he was an airframe mechanic for cargo jets. Man, that guy was so overqualified. He was ostensibly a plumber, but maintained this elaborate boiler system we had in our last house back east.
If you get somebody good, your life will be improved immeasurably. :)
Or, at least you won't be tearing your hair out.