There are two types of complaints; misconduct and overcharging.
If a client believes their lawyer’s behaviour falls short of the expected standard of competence and diligence of a reasonable lawyer, then the client can complain to the Commissioner about that behaviour. So too can a third party who is impacted by the lawyer's conduct.
If a client believes their lawyer has overcharged them, then the client can complain to the Commissioner. So too can a third party who is otherwise impacted by the lawyer's fees.
If the Commissioner receives an overcharging complaint within two years of the relevant bill (invoice), then he must investigate it. Outside of this period he may investigate it, but is not obliged to do so.
Regardless of the amount in dispute, the Commissioner may recommend a reduction of, or a refund of some or all of, the legal fees billed to the client. A recommendation made by the Commissioner is not binding.
If the recommendation is not accepted, and if the amount in dispute is less than $10,000, then the Commissioner may (having first gone through a specified process) make a binding determination as to whether or not there has been overcharging and if so, the amount of the overcharge.
For further information, refer to the Law Society's fact sheets about legal costs and your rights.