In terms of the obligations of an agent to their client under Part 3 of the Code, you should be aware of the provisions of clause 3.6:

A migration agent must ensure that clients have access to an interpreter if necessary. 
Often there are circumstances where a professional interpreter is beyond the means of the client and a family or friend undertakes the interpreting.  This should be disclosed to DIAC by way of explanation in the form of either a letter or statutory declaration and then included in the documents submitted with the application. If it turns out the interpretation was not 100% accurate then your having have notified DIAC at the beginning, that the interpreting was not done by a NAATI accredited interpreter would ordinarily get a sympathetic hearing from a case officer if an amended but corrected translation is then submitted. In a perfect world one does one’s best to get accurate translating and interpreting done but this does not always happen.  The writer had the experience in an MRT case of an Australian CPA accountant of Chinese origin having done all the interpreting in a business visa matter at the visa stage but got the interpreting wrong (he was not NAATA accredited).  At the MRT hearing the accountant gave sworn evidence that he got the translation wrong because his clients were from north China and had an accent which was unfamiliar to him.  The MRT accepted that explanation.