As quoted previously - http://law.ato.gov.au/atolaw/view.htm?docid=ITR/IT2167/NAT/ATO/00001 :
I understand that (18) is easy to do, but (19) says you cannot "dress it up" to look like (18).
Perhaps I'm over-cautious due to this being my first house, but if, for example, the lodger caused...