I always treat it like a business transaction.
When selling.
Raise an invoice inc GST
When the invoice is paid submit the transfer documents.
Keep the customer informed as they tend to be a bit nervous.
When buying.
Request invoice.
Send new registrant details.
Pay invoice.
Await transfer.
If they don't transfer (which hasn't happened in 6 years of trading) then I suppose I start to worry and send the boys round.
Before any transaction I like to know whom I am dealing with so a bit of prior investigation is always in order. Also it is good to have a bit of patience as transfers in .au land don't happen overnight and the process is a bit painful.
Lemon