If you have a character with Enchanting who can DE Northrend greens, this most definitely isn’t the case.
My wife used this method to amass gold until she felt bored. It’s practically a cheat code for infinite gold. I used it as well while I was notching Blacksmithing.
The “secret” lies in the almighty Notched Cobalt War Axe. You learn this recipe from the trainer at about skill level 400 (not sure the exact point, just wowhead the item to be sure). It costs 10 cobalt bars to make one axe.
On my server, cobalt ore/bars go for roughly 1g apiece on the AH. If you’re careful, you can probably build up quite a stock for lower (50-80s per ore) since cobalt generally isn’t in high demand (jewelcrafters prospect saronite for better results). 1 cobalt bar is made from 1 cobalt ore so they are equivalent if you have a miner as well.
So, 1 axe costs 10g tops.
The axe disenchants into the following:
75% chance of 1-2 Greater Cosmic Essence (so average = 3/2 = 1.5)
20% chance of 2-5 Infinite Dust (so average = 7/2 = 3.5)
5% chance of 1 Dream Shard
On my server, Greater Cosmic sells for about 12g, Infinite Dust about 5g, and Dream Shards for minimum 15g.
So, your expected value from disenchanting a single axe is:
(0.75*1.5*12) + (0.2*3.5*5) + (0.05*1*15) = 17.75g.
This means that you can expect a minimum of 7.75g profit per every 10g investment. Furthermore, note that you can never lose money with this since the worst possible results from the disenchanting already sell for above 10g (1 Greater Cosmic/2 Infinite Dust/1 Dream Shard).
So, just buy up all the cheap cobalt, make tons of these axes on your blacksmith and de them all. Send the resultant mats to your AH character and sell them off whenever the market is good. Enchanting mats don’t even have a list price so feel free to put whatever price you want for 48 hours, and enchants are always in demand especially with all the free gear available nowadays. As usual check the price differential between Lesser and Greater Cosmic Essences and split/combine them accordingly.
Why farm when you can almost double your gold with a few clicks?