Alright, so, I don't know if any other servers do this, but on mine they do.
They'll post a message in trade like:
WTB 10k honor (gems) - 120g/pc
WTB emblems (gems) - 120g/pc
WTB ALL UNCUT EPIC GEMS - 120g/pc
Alright, so basically, all you're doing is buying gems at a lower price (usually lower than the Auction House), cutting, and reselling the gems.
The highest profit gem cuts (clearly server dependent) are typically the following:
Design: Runed Cardinal Ruby - Item - World of Warcraft
Design: Forceful Eye of Zul - Item - World of Warcraft
Design: Enduring Eye of Zul - Item - World of Warcraft
Design: Bright Cardinal Ruby - Item - World of Warcraft
Design: Shifting Dreadstone - Item - World of Warcraft
Design: Deadly Ametrine - Item - World of Warcraft
Design: Durable Ametrine - Item - World of Warcraft
Design: Solid Majestic Zircon - Item - World of Warcraft
Average sale price per gems above: 160-200g (on my server)
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You can get all of these patterns by getting Dalaran Jewelcrafting Tokens. These can be received once a day from doing the JC daily, and also from buying Titanium Powder - Item - World of Warcraft from the Auction House (also prospectable from Titanium Ore, but usually costs less to buy it direct).
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That's it.
Thanks for reading!