It is very important to find a well-established and reliable air conditioning company that possesses valid qualified licences accredited by the Australian authorities and is also an authorised dealer of major air conditioner brands.
For a peace of mind, find AC company that is able to provide services from advice, design, supply, installation, maintenance and also qualified to provide repairs service. Ask about the warranty period for their services and areas included in the warranty, eg. installation work. Also, it is important to know their respond time when you need them.