I "actively watch" and receive e-mails from AirTran for "sales." This is the route I follow:
1. Watch my already booked airfares...if it comes down, I move on.
2. Go onto AirTran's website, and enter in my travel information (as though I'm making a new ressie) with the same number of passengers as per my original booking. (This is very important, because if you call down and ask for the credit, but there are only 3 seats available for that particular lowered fare, but you booked for 5 people, you cannot receive the credit.)
3. I calculate what the price difference would be. For example, my first round of receiving credit went something like this (I booked one way flights, which I don't normally do, but had to this time):
-original flight: ($104.80/person x 6 people in my travel party) + ($6 seat assignment x 6 ppl) = $664.80
-fare decrease: ($94.80/person x 6 ppl) - ($104.80/person x 6 ppl) = should receive a $60 credit
[The rep tried to credit me $96, but I knew better: she had canceled my ressie entirely, re-booked me at the new price, and lost my assigned seats. I informed her of this, so she was lucky enough to snag our seats back (I wasn't that lucky for my last trip in Oct. 2011, but was compensated with extra credits). Another time, my ressie showed I owed $60, because the rep charged me the $15/person fee for booking over the phone, which I did not. Needless to say, I got that taken care of quickly and efficiently. Bottom line, be informed and prepared before talking to any rep.]
4. I then call 1-800-AIR-TRAN: #3 (All other Inquiries)-> #1 (Change Existing Reservation) -> wait for "travel agent."
5. When speaking with the rep, I say, "I have an existing reservation, but noticed the airfare came down, do you honor the difference?" (which I know they do, but like the reassurance). The rep then checks, and if the fare is available for my entire party, I am issued a "credit." This airline "credit" expires 1 year from issue and can be used toward: future flights, baggage fees, seat upgrades & assignments. Your reservation # is your "credit" #, so be sure to hold onto it.
As long as you're not changing flights or days of travel, you will not incur the $75 change fee.
I am not sure how the Southwest/AirTran merger will effect these airline credits, so I always use ours for baggage fees & once in awhile, seat upgrades (Business Class anyone?)!
I hope this helps!!
P.S. I would've posted 4.5 hrs. ago, but my internet was down...