If a business contacts you, you can check to see if they are on the Register of Participants, which means that they have been accredited by the ESC.
If an installer contacts you at your house or business, ask to see their ID which should feature their name, the name of the accredited businesses they work for, and the business address. Be aware however, that the Energy Saver Incentive is not the only program in Victoria offering energy efficiency products and services to consumers. Other programs, such as those within local councils, also offer energy-saving light globes or showerhead exchange programs.
Remember, you do not have to let anyone into your house or business if you feel uncomfortable.