This is another hypothesis post, so here goes. When should you be aggressive?
Let's look at the big consumable markets: Potions, Flasks, Gems and food. Everyone always needs these for raiding.
If I listed flasks a month ago, would they sell? Probably not. Why? People aren't raiding yet. If I listed rare quality gems a month ago, would they sell? Probably not! Why? Again, people aren't raiding, and aren't getting new gear.
Now is a great time for these markets; people are always getting new gear, wiping on raids, and downing bosses (although not necessarily in that order). Prime time to capitalize.
Say a raid goes to fight Magmaw, and spends 3 hours on that boss. They average 5 attempts per hour, which is 15 per night. They get it down on the last attempt. Let's break it down:
25 man - 15 attempts: 25 X 15 = 375 food pieces they require. 75 flasks, 375 potions (assuming everyone uses a potion every fight, like they should), and maybe 12 gems required.
Add it all up and you have major profits. Of course, not everyone will buy from you, but THIS is the EXACT reason why raid nights are so profitable. GO FORTH AND EXPLOIT.
Note: leg armors/spellthreads are consumables that get replaced often as well, but they're only on one piece of gear. Ergo, they get replaced about 1/10th as often as you regem something.