ahjay. I do not think it has anything to do with the ASX as they...

ahjay.

I do not think it has anything to do with the ASX as they trade 3 places all trades are registered there.
They cannot control broker to broker or person to person trades,
I could say to you I will give you half a point more or half a point less for your shares and if you agree the trade has to be registered and you control the SP without trading on the ASX at that time.
That is why it is called a free market. IMO