All you need to do is go up into the attic and inspect their work. Misaligned ducts. Untapped joints. Hot and cold air blowing out of gaps that would take a small amount of tape to seal.
Shameful. And particularly shameful when they claim to be professionals and knowing so much.
If a guy can't see there's an inch gap in a duct, and goes on with his work, he's a true idiot, an unprofessional, or someone who TRULY doesn't give a shit.
STeve