That's way better than taking a chance with a stranger. I can skip the bidding process because I know they'll treat me fairly. They'll do good work and the pricing will be fair.

Most contractors won't deliberately jeopardize their networks of trust. That's their bread and butter, especially in an economic downturn. If unexpected problems occur that they might have caused, they'll usually voluntarily eat the cost. (I usually pay that cost myself if they're already giving me a really good deal.)

It doesn't always work out. I have two mechanics that I use only as backup plans. One is a friend and the other a referral, that I'll only use as a backup plan. (I doubt their competencies.) Even with those, I feel like my experience was probably better than picking a shop at random.

The HVAC shop in this scenario doesn't sound like a bad one. He's responsive and even came out to the home on a Sunday evening. He's obviously not deliberately trying to create more work for himself by deliberately breaking things or recommending work that doesn't need to be done. If they had fixed it before they left the first time and charged for it in then, no one would have complained. I would probably pay him a couple hundred to fix the valve and thank him for being cooperative.

That said, I do find it odd that he got defensive when suggested that he might have caused the problem. He should be grateful he didn't kill anyone. I'd have to see the situation for myself to form a definitive opinion.