I organised the $300 service of our ducted heating through Gaschill.
As we had no airflow to areas of our house and parts of the floor were getting warm, I suspected damage to ducting under the floor. Gaschill came out, told me my ducts were fine (showing me photos of some ducting) and that my old unit needed to be replaced, quoting me $3800.
Less than two weeks later another company I'd organised came out and within 15 minutes of being under the house came out and showed me a photo of a section of destroyed ducting, saying a few hundred dollars would cover the repairs required.
When I contacted Gaschill they were adamant that they had done everything above board, so I don't even know if they did anything to check the heating unit at all, and were just happy to charge me for a new unit that wouldn't have worked anyway thanks to the damaged ducting.