a party must have notice of the case they have to answer.
each party must have the opportunity of adequately stating their case, including sufficient time to prepare their case, and correcting or contradicting any relevant statement prejudicial to their case. Note that there is no requirement for the Commissioner to ensure a party takes advantage of that opportunity.
a party must not be heard behind the back of the other party.
relevant documents which are considered by the hearing officer should be disclosed to the parties.
hearing officers must not be a judge in their own cause. Thus, a hearing officer must declare any interest they have in the subject matter of the dispute. This may (inter alia) disqualify a hearing officer from hearing a substantive s59 opposition where that officer was directly involved in the examination of the application.
the hearing officer must act fairly, in good faith and in a judicial temper.

The rules of natural justice require that not only should justice be done, but that it should be seen to be done.

Case Law

The High Court in Johnson v Johnson [2000] HCA 48 heard an appeal based on judicial bias, following the judge in question stating that he would be placing greater weight on independent evidence, rather than the testimony of the two parties in a Family Court matter. The judgement provides guidance on the appearance of bias:

"It has been established by a series of decisions of this Court that the test to be applied in Australia in determining whether a judge is disqualified by reason of the appearance of bias (which, in the present case, was said to take the form of prejudgment) is whether a fair-minded lay observer might reasonably apprehend that the judge might not bring an impartial and unprejudiced mind to the resolution of the question the judge is required to decide"

and

"At the same time, two things need to be remembered: the observer is taken to be reasonable; and the person being observed is ‘a professional judge whose training, tradition and oath or affirmation require [the judge] to discard the irrelevant, the immaterial and the prejudicial’”.

The court also noted that judges who express tentative views are not on that account alone to be taken to indicate prejudgment. In the court's view, judges are not expected to wait until the end of a case before they start thinking about the issues, or to sit mute while evidence is advanced and arguments are presented. On the contrary, they will often form tentative opinions on matters in issue, and counsel are usually assisted by hearing those opinions, and being given an opportunity to deal with them.

"At the trial level, modern judges, responding to a need for more active case management, intervene in the conduct of cases to an extent that may surprise a person who came to court expecting a judge to remain, until the moment of pronouncement of judgment, as inscrutable as the Sphinx. In Vakauta v Kelly [1989] HCA 44 Brennan, Deane and Gaudron JJ, referring both to trial and appellate proceedings, spoke of ‘the dialogue between Bench and Bar which is so helpful in the identification of real issues and real problems in a particular case.’”