If you have a stack of 20 of something that sells for, say, 10 gold, don’t sell it as a single stack of 20. Sell it as four stacks of 5, and price each stack at 3.5 gold (for example). You’ll earn 14 gold that way instead of 10. Also, don’t list too many stacks of items at one time.
In some cases, when I’ve checked the current prices for an item, I find one or more sellers who are pricing it drastically lower than the others. For example, I might be looking at Medium Hides. Player A might be listing 5 of them for 5s, Player B might be listing 5 for 6s, and Players C-F listing them for 9s each. In those cases, I’ll often buy out Player A and B, then immediately re-list those stacks of hides for 8s or 9s. That now, at least temporarily, makes the going rate for a stack of 5 Medium Hides 8-9s, and since mine are the lowest priced, they’ll probably sell first. In the process, I make 5-6s just for re-listing them. But that’s just an example. You can find many more-expensive items in the same situation. Just be careful that the price you’re paying for the items isn’t more than they typically sell for on your server. That’s where the Auctioneer add-on can help a lot. It tracks the current pricing in the Auction House for you and lets you know what you should expect to get/pay for an item based on your server’s market.
I’ve done a little of this with a lower-level character in my account and I can vouch for the fact that disenchanting CAN be profitable. One guide describes this as the “certainly least profitable gathering skill” though I’m not so sure, for a reason I will explain momentarily. If you search the Auction House for green, blue, and purple items, you will find that there are plenty of lower-level items available for sale reasonably cheaply. I’ve seen some mediocre green weapons and armor selling for prices of 20 silver or less at buyout. If you buy those items and disenchant them, my experience has been that I often (though not always) end up getting ingredients that can be sold for far more than I paid for the item. I suspect that if an enchanter made a regular practice of buying up all the cheap green items in the Auction House, disenchanting them, and selling the results, he’d make a decent profit at minimal risk to himself.
Similarly, an enchanter who happens to loot a “binds on pick up” item they can’t use may find that disenchanting that item offers a better reward than dumping it on an NPC vendor. I’ve seen this strategy used in dungeon crawling. Each time a player loots an item that binds on pickup that no one can use, they roll for it. The enchanter disenchants it for the winner, so that the winner can sell the ingredients later.
The Scarlet Monastery in Horde lands contains multiple instances. It’s possible to solo these instances if you’re at a high enough level (most of the mobs inside are in the level 35-40 range). It’s said that if you go through there and disenchant the items you loot from the mobs, you can easily collect a lot of Small Radiant Shards, Large Glowing Shards, and other useful items. These can be sold on the auction house for a lot of gold. The author of this particular strategy says he was able to make about 60 gold in an hour by disenchanting and selling stuff from these instances.
Another guide mentions that if you go in the Graveyard instance, there is a torturer in the first room who spawns a chest with 3g worth of green items in it every time. If you leave reset the instance, and repeat, you can collect a lot of good loot. (At least, that’s what the author of that guide says. Personally, I think you run the risk of this being deemed an “exploit” by Blizzard.)
In the Un’Goro Crater, in the northeast corner of the map, you’ll find a cave filled with gorillas. They’re all level 51-55. A level 60 warrior said that after 1 hour there, he returned with 19 tufts of Gorilla Hair, 18 Gorilla Fangs, 2 empty barrels, 3 Coarse Gorilla Hairs, 1 green item (leather pants), and 12 Un’Goro Soils. He was able to sell all this on his server for around 8gp. On my server, I’ve seen the soil sell for more than he got, so this might be very profitable on some servers.
Supposedly in the DM East instance there is a Rich Thorium Vein. If you mine that vein, reset the instance, mine it again, etc., you can supposedly get quite a bit of Thorium Ore and rare gems. On the other hand, the author of this particular strategy claims that Blizzard banned his account for doing this, so I don’t recommend it.