First of all let me say this: If you are having problems with your heater or A/C go to Home Depot or Lowes and buy a thermostat ($10-$60). Installing it consists of disconnecting 2 wires from the old thermostat on your wall, then connecting those 2 wires to the new thermostat. In many cases this will solve your problem. If not, return the thermostat and call somebody else.
I called Torrance Plumbing to fix my wall heater (read total value when new just a couple of years ago: $400). They told me there was a minimum charge of $125 which I agreed to thinking that would include any minor work. Once they arrived and decided it was the thermostat they wanted another $60 for that (apparently the $125 minimum is for showing up and doing a "diagnostic check". The result was I had to pay $185 for what was probably a $30-$40 thermostat that I could have installed myself in 10 minutes. Keep in mind that this was a wall heater. They did not have to go up in the attic or under the house. It was all right there in front of them. When I complained, the owner tried to explain to me they had actually undercharged me for the less than an hour their tech was here.