One of the easiest ways to make gold in World of Warcraft is by selling limited supply items that other players really need. You need to go to certain locations, find special vendors, buy the rare recipes, essences, items, etc. And then run to the auction house and sell them for a profit.
Usually, when talking to a vendor, you'll see a (1) or (2) next to rare items. This means there are only one or two of that particular item left for the time being. Sometimes, you can buy what's left and sell it at the auction house for a profit. And, if you have time, you can stick around and wait a few minutes for the items to respawn and buy some more from the vendor!
Some limited supply items in World of Warcraft are worth more than others. It all depends on how crowded your server is and how much in-demand that particular item really is. Here's a list of some of the special sellers you can visit to find certain items that will sell for a lot of gold:
O Hinterlands — Visit Ruppo, who lives in the hills in the Northeast area of Aerie Peak. He sometimes sells the engineering plan mithril dragonling for about 40 silver. You can probably sell it for around 2-4 gold, depending on your server. Also be on the look out for ironfeather shoulder patterns, which can sometimes be found in that area. Resell it for 2-3 gold.
O For alchemy, Look for the elixir of shadow power recipe in Stormwind. It's sold by the sponsor Maria Lumere in the Mage Quarter. Only one is sold at a time, so you need to keep checking back until it respawns. You can sell it for at least 6 gold.
O Elixir of superior defense and free action pot can both be found in Ogrimmar, Stranglethorn Vale, and Ironforge. Look for the vendors Kor'geld, Soolie Berryfizz, and Vosur Brakthel respectively (although Kor'geld can sometimes be found in Stranglethorn Vale.
O You can get shadow oil in Duskwood and Thousand Needles from the vendors Bliztik and Montarr. On a good server World of Warcraft server, you can sell each one for around 100-200% more at the auction house than what you pay for it! You'll definitely want to stack up on this recipe.
O A limited supply blacksmith recipe is the golden scale coif. You can find it at Taranis by visiting either Krinkle Goodsteel or Trenton Lighthammer.
O Visit Stranglethorn Vale for the massive iron ax recipe. It's sometimes sold by vendors Hemet Nesingwary and Vharr.
O While in Stranglethorn Vale, visit Zarena Cromwind for moonsteel broadsword recipe. You can sell each one for 1-3 gold at the World of Warcraft auction house.
O You can find a couple of limited supply leatherworking items in the Blackrock Depths. Look for Lokhtos Darkbargainer for the black dragonscale boots and corehound boots patterns. Also look for Plugger Spazzring for black dragonscale breastplate.
O In Winterspring, look for the goods supplies vendor Qia in the goblin town of Everlook for the frostsaber boots pattern. You may also be able to find the mooncloth recipe if you stick around for awhile!
O In the Wetlands and Hillsbrad Foothills, you can get the green leather armor pattern from George Candarte and Wenna Silkbeard respectively.
O For tailoring patterns, you can check out Super-Seller 680 in Desolace for a crimson cloak pattern, dark silk shirt, and enchanter's cowl.
O In Moonglade, visit Lorelae Wintersong for felcloth pants and Darnall for a runecloth robe pattern. Darnall also sometimes sells patterns for runecloth boots and cloaks.
O Visit Outfitter Eric in Ironforge for the following patterns: tuxedo pants, tuxedo shirt, tuxedo jacket, and lavender mageweave shirt.
These are just some examples of limited supply items you can find in World of Warcraft. Again, how much gold you actually earn from selling them depends on the server you're on, the time of day, and demand. Hopefully, you'll learn enough from this guide to make all the gold you need!