Three things: isn’t this for the new business owner to sort out, at their cost? And if the person working for $10 is a resident would the activity not be covered under your general insurance? A simple check with the insurer would confirm such. And getting an ABN is a pretty standard free thing and very easy to get, so they should just register to get one. But for a tiny $120 a year in income that might be swallowed up in end of year extra accounting fees to keep the ATO on-side.