You can also if you are 30 days out from travel and within 24 hours of the booking, call Qantas to ask for the fare code and pay the difference without penalty to the next highest (often Q) if your booking is in /E/. Which is often just a few dollars. Also you can get a hint when booking a popular route such as MEL/SYD if you see a bunch of fares for a low price and then some a few dollars more, the few dollars more fares will not be in /E/.

You can find the fare code AFTER booking on manage my booking (QF), Finnair, Qatar etc.

Tragically the eticket receipt does not mention the fare basis or booking code - which makes it extremely hard to look up the fare rules.