ARIA is the official charts company in Australia. This is how the ARIA charts are calculated in Australia.
ARIA charts in Australia includes both physical sales, digital downloads sales and music streaming (but doesn’t disclose the exact ratio in which music streaming is included).
Here you can see the full list of accepted retailers.
ARIA compiles the data for weekly charts, but doesn’t state whether multiple sales by a single consumer is included or not.
It seems like there is a big grey area and is open for manipulation.