I know this isn't a big secret, but I just wanted to spread some knowledge that has netted me a decent amount of gold this week. Anyone that has a twink character understands that there are some low level items that are just ridiculously overpriced.
For explanation purposes I'll focus on level 19 battleground items.
Sentry Cloak
Keller's Girdle
Dark weave Britches
Magefist Gloves
Asassian's Blade
Twisted Chanter's Staff
Tree Bark jacket
Feet of the Lynx
Little Timmy's Peashooter
Meadow Ring of Eluding
Throat Piercers
When I search for the items I usually leave the item name blank. Level 11-19. Rare.
Above are a few examples of what I search for between the alliance and horde auction houses. The different faction auction houses on my server at least are nowhere near the same prices for items.
Like i said this isn't a secret or uber money guide, just a idea.