The inventory in a GDS is priced at a set rate under a certain fare class, the inventory needs to be exhausted for it to go to a higher fare class, it doesn't happen any other way. I'm sure Amadeus, Sabre and Galileo, don't have the technology or would even care.
Thought I might just chime in here with my 2c.
Currently work in the industry. It grinds my gears when everyone breaks out their stories of this 'phenomena' happening to them (or more often than not, their 'friend'). And nearly every story mentions "looking at it over several days/weeks".
That's the first problem - time. The facts are that an airline releases availability that is displayed in REAL TIME on a GDS. Expedia pulls it. Webjet pulls it. Flight Centre pulls it. Occasionally I've seen the data cached on some sites, leading to "why is x.com cheaper thay y.com" Chances are you'll get to the last page and "your price has been updated." All airlines during the week will run some sort of yield management check throughout the week that might mess with you availability view, but that usually only lasts a couple of hours and is rare.
Let's take QF as an example. Normally when booking directly through a GDS information is O4, Q9, S9 when doing a search for economy availability. O for example has at least 4 seats available that can be sold, and so on up the chain. Usually once O sells enough, it will read O 0, or O C and you'll have to sell Q, the next cheapest available. If it reads C, it's closed, and that seat class can no longer be sold. Suddenly your fare will jump at least $50. However if it's 0, it could be waitlisted, and some seats might become available again. Generally speaking you can't hold waitlist on online agency booking sites.
Me, and thousands of agents around the country book seats in. Basically "hold them in" until they're paid for. But let's say they're not paid for, and the reservation reaches it payment deadline (TTL). Usually the airline cancels out your 'hold', and they're released back into the wild to be booked again by the next person to grab them in real time.
And therein, I believe, lies the "mystery" of how they change price to become cheaper again the following day. Most people booking online don't have the ability to sell (hold) a seat without paying for it immediately. But travel agents can. Thousands of them around Australia, holding in thousands of seats of thousands of aircraft, a large percentage of which may not result in an eticket being issued.
Additionally, most people don't have access to, or can see the "sales restriction" paragraph of a fare rule (that corresponds to the classes spoken about above". They're not aware of the end of an impending sale, unless the airline/online agency broadcasts it. So your fare is no longer available "magically" the day after you were just looking at it.
Webjet I'm 99% certain doesn't "hold" anything for you for 30 minutes as it purports. It just plays the odds game that no one else is going to take the last two seats in O class on that Qantas flight, and if it loses, so what, it's charged you a nice booking fee and will make enough money off of the next booker to cover the potential minimal loss of moving you up to the next booking class. And in the US I know their pricing and fare basis's also change depending on how close you on to the departure date. Not to mention that the exchange rate fluctuates and prices are updated once a week by Iata, which can mean a few dollars shift too.
However, on the flip side, and something I can't disprove - I could see a lot of websites possibly altering the data after it's presented to them by the GDS. Maybe they can track it via cookies and add $50 onto the fare displayed to your browser, who knows. That, and the fact that certain companies might have better contracts with certain airlines to get them special fares or better commissions, allowing them to undercut others.
My advice- if you're booking retail, find a good travel agent you can trust and go through them. If they're worth their cheese, they'll know the actual ticketing deadline of a ticket and can hold it. And the beauty of the system is if you find it cheaper online before booking, they'll price beat it.
