Visa applicants are permitted to lodge their own applications. But if you are not familiar with the requirements and the regulations, then it’s always better to lodge an application using a registered migration agent.
All registered migration agents who are operating in Australia must have a registered MARN number and you can always find out more information about migration agents by visiting the website of the government’s Migration Agents Registration Authority (MARA):
To protect yourself against fraud by migration agents always check the agents MARN number.