We went through this with a neice who wanted to visit her father in Australia. As she was a minor, all sorts of info had to be provided including return tickets and a letter of credit for her support. I've had to prove that I have a return ticket for my own new Australian visa. When I got it, the comment was made....'your credit card has a high enough limit'. I took that to mean they believed I would be able to feed and house myself. Australia welcomes you to come and go! I don't blame them!