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MageshadowHave you ever heard of
Stratholme Lilies? have you ever seen it at the auction house? My best guess is that you haven't, why? Because this item is simply rare. It's not hard to obtain but not many people know where to obtain it. It's relatively easy and by snagging yourself 4-5 of them you'll be able to make some nice profit at the auction house.

First and foremost I'll tell you where you're able to obtain Stratholme Lilies. You can buy them from Sophie Aaren in The Culling of Stratholme. That's right an old Wrath of The lich King dungeon. You have to go back there, but trust me it's well worth it.
First and foremost you can get here easily by getting a portal to Dalaran then taking the portal to Tanaris. Proceed to take the dragon outside the cave down into it's depths. From there locate The Culling of Stratholme. Now once you're inside you don't have to start any of the events simply run in, locate the NPC. To find her shop simply enter the city and keep right till you reach Festival Lane. You have to buy the lillies before the event starts so don't start it!!
One of the best parts is that Sophies not only sells Stratholme Lilies, but a whole bunch of other flowers which I will list below:
Beautiful Wildflowers
Black Rose
Bouquet of Black Roses
Bouquet of White Roses
Simple Wildflowers
Red Rose
Now since literally no one will have these flowers at the AH you'll be able to name your own price. I typically sell the lilies at 200g/per, that's 180g profit per lilies. I simply love utilizing this strategy because I also get the other flowers which I listed above. They don't yield as much profit as the lilies, but profit is good nonetheless.