What are some criteria to get an Australian PhD scholarship? I want to apply for a PhD in Australia and I wrote a professor (who has an open position) with my CV. He was very positive in his mail and encouraged me to apply for that position. Now I want to know who is the decision-maker in taking a student and offering funds? I mean is it like the professor asks people to apply but the ultimate decision-maker is the university itself? Or the professor can take anyone if he wants to. What is most likely to be in Australia?
Also, is it true the scholarship committee focuses solely on GPA, rather than research work? I mean is it possible if the GPA is not high but research experience and works are excellent?
For Australia, both the supervisor and the university might reject a PhD student.  Universities may often reject PhD students for inadequate language ability even if the supervisor wants the student.  These decisions are based on a threshold, not based on who else applies.
Some supervisors have funding they can use to pay PhD students at their discretion, but most PhD students are funded through a university program.  The fact that a position has been advertised does not mean the supervisor necessarily has funding for that position.  For funding by a university, research experience is essential.  Marks (not called GPA in Australia) are also considered.  There is a fixed amount of funding available, so decisions depend on who else applies.