using an agent is not illegal. In Thailand it is just business. If the authorities decided it was illegal to use an agent, then they would have to prosecute half of the expats living here. However, make your own mind up and do what you are comfortable with.
Nobody was talking about taxes until you raised it! The subject was about how unfair Australia was making it for their citizens to retire overseas by making them live there for two years to qualify for something they are entitled to! It's typical for someone to divert the point of a debate to point out an unrelated matter rather than admit the injustice!