I've been very happy with the service they've provided over the years.
I've used D & M Heating & Air Conditioning for almost thirteen years. They do my furnace and air conditioner maintenance on a yearly basis. When it came time to replace those units, I contacted them, asked for information, and asked for somebody to come out and do an assessment to make sure I was looking at the correctly sized unit for my house.
I was happy with the discussion I had. They didn't try and sell me a bigger unit for more money if I didn't need it. The people doing the installation were on time, completed it within the time they said they would, and were very courteous. They were very neat and cleaned up after themselves. They also explained the operation of the thermostat to me before they left so that I had a good understanding of how it worked.