All .AU domain names must be associated to a registered Australian entity (company, business, organisation, etc). This entity will become the legal owner of the domain name and as such MUST be your client's business, not yours. All .AU rules and policies are set and governed by the domain name registry for .AU domains - auDa.
We, as accredited registrars, should be fully aware and must strictly adhere to all such registry policies. Otherwise, the domain registration will be rejected.