What are some criteria to get an Australian PhD scholarship?
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.