Thanks RichardMel. I agree the conditions were stated in advance. However, in my previous case, I wanted to purchase flights to a different location that would still have been greater than the original fare and the same conditions but these were not accessible. Also, I don't understand why Qantas (and probably other airlines) give a voucher less flexibility than the paying by cash. I assume it's to discourage cancellations. I think I'll wait until the last minute in case Qantas cancels my flights and I can get a cash refund.
To the 2nd point I would say this - my personal view is this is a technical limitation of the kuldgey way QF implemented vouchers/credits on top of Amadeus. For example I've had vouchers on other airlines and never had this particular condition or issue before.
So to the first point let me see if I understand the situation correctly.
You have a voucher for a certain value, let's say $500. A credit voucher from a canceled flight/booking? And it was on a route like MEL-SYD as example Now if you want to redeem that $500 value on a different route, say SYD-OOL, you can see fares of say $550 but when you go to use the voucher you're not offered those, but you're offered a higher fare, such as $700?
If I read this correctly I can think of one reason for this potentially as annoying as it is.
With some fare types, specially less flexible ones, such as those in red-e-deal and discounted Economy categories, say booked in Q or N or O(and others), one of the conditions usually is that changing the flights must go to a higher fare booking buket, usually the next highest. One of those legacy things.
So let's say from my made up example above, your MEL-SYD $500 credit was for a fare booked in O class, you go to rebook a new fare, yes on a different route, and O class fares are out there for $550, but the original fare conditions is forcing you up to say a Q fare or something, which shows as $700.
I've seen this in the past. I had thought QF had relaxed things somewhat during covid (and while change fees have been waived they do still say "A fare difference may be payable" which is a bit of a catchall)... it may well be worth calling (ugh) and asking specifically why you can't access the fares you see.
I just see this with my own voucher actually. one was booked in K class for a sector... even though K class is available on the route I picked (I'm looking at the same sector, different dates actually) I'm being offered the higher Q class fare with the voucher. And since my original fare was booked as a K (Flex) fare, I'm not offered anything discounted below that for the same reason, even if, for example, I might select a Business fare on the return and the entire total is higher than the original fare.
so this is a thing. it is very frustrating (and no, it is not very fare.. I mean fair).