Before you hire a heating and air contractor, do a quick check with the Construction Industries Board. Their website has an active list of licensed contractors. This will ensure that they have the right insurance. But make note of what they're licensed for. If it's a "journeyman" that means they can do the work, but they must be working under a "contractor". When they give you the contract, it should have the name of the contractor on it.
If you have a complaint against a heating and air guy you can also call them at (405) 271-5217.