I Fly, I think you have answered your own question.
Centaurus
It can be open slather to the unscrupulous to fake instrument flight time because there is no way CASA can detect it. From talking to CASA personnel there is no knowledge of anyone ever been caught logging false instrument flight time. Not because it does not happen - but because it is impossible to police.
No way CASA can detect it? Impossible to Police?
If CASA actually got out of the office occasionally and conducted the safety audits they they are in existence to perform they would discover all sorts of things about GA. You cannot find if you don't look.
There are more and more GA types entering CASA as FOI's. Some friends of mine for example. When I chat to them about why they don't look at issues that they are personally well aware of they tell me that they have no resources. Read time and money. Why is this? FOI's are well paid by GA standards, how do they fill their days.
Back to the issue of logged IF. It is a simple matter to choose an entry from a candidates log book, request a report from the Bureau of Met for forecast and actual on that day, request tower logs for the time in question. Then put the whole lot together. If it was a charter flight the FPL should be on record with the operator.
So all of these items can be checked. On flights originating or terminating at airports with open towers it is quite simple. As I look out my window today, all I see is blue, so anyone logging IF in my neck of the woods would be easy to catch out.
The point is CASA may have told you
Centaurus that it is "impossible to police". Clearly that is not true but there has to be a will, then they will find the way.