FYI, the people working the 131 number are only call centre employees with very basic knowledge of the rules. They're not immigration workers with any sort of official designation or authority. They have on several occasions provided me with very wrong advice
My experiences over the past 5 years have indicated that Aussie immigration is very strict, and very much on top of everything, even as far as keeping tabs on individuals when you wouldn't expect them to.
An ex-girlfriend of mine had a work visa and the working portion of it had just expired. She still had the right to be here, but could no longer be employed. Her employer wanted her to stay on for ONE extra day due to it being a busy time. Two immigration workers showed up later in the morning and asked for her. They had a short and friendly chat about her circumstances, then presented the business a $10,000 fine. There was no particular reason for immigration to be checking up, she had always followed the rules until that day.
Living on the Gold Coast, there's a lot of transients and tourist here, so you hear a lot of visa stories. It's quite common to hear of foreigners over staying by a couple of days, and usually after about a week (or less) immigration is phoning around and searching for them. At the very least these people are given a couple of days to leave and banned from re-entering the country for several years.
I've personally had a legitimate holiday visa cancelled simply because the immigration officer decided I was "no longer here for holiday purposes" (I was with my Aussie girlfriend travelling on a brief holiday to Canada
, and had already been travelling in Australia for quite some time). They cancelled my visa on the spot, warned me that I could not return on any tourist-class visa for a couple of years. My visa and paperwork was all current
, I still had plenty of time left.
It took me 6 months in Canada
to finally sort out a new visa and have it approved (prospective marriage class).
Bottom line, don't F with immigration. It's not worth the hassle.