I received $1000 and was asked to send it back. How does this scam work?

Definitely Australian. 'Netbank' is the proprietary name given to internet banking by the Commonwealth Bank of Australia. I use it myself, its interface is very simple to use.

Money transfer to other bank accounts can be via Direct Credit to 'anyone', even to foreign bank accounts. Company Invoices can be paid using that same system or by a slightly separate system called BPay.

Paying money by cheque is now practically non-existent in Australia. I don't think I have written one in several years.

https://www.npr.org/2019/06/26/736352315/episode-922-the-cos...