Everyone is right. I've had both great service and poor service. David is very friendly and does a good job when he comes. However, he does a poor job returning calls. And he did stop by without going into the attic and assumed the issue was with my dirty filters and thought the units had "froze out" He had to return the next day and fix the actual problem. I have received great service from him and he has never tried to rip me off or do excessive unwarranted work.
I think what happened is he got too busy for his own good. When he initially serviced my place, he returned calls, came on time and did great work. As they got increasingly busy, the level of service dropped. Still in terms of being honest and ethical, David is definitely a stand up guy. However, he needs to be more professional and return calls and communicate better.
That being said, I don't know many honest and ethical HVAC guys. I would still use and recommend Sweet Mountain Air because at least you know you won't get ripped off even if he doesn't return calls or show up on time.