As an example, I know that prices for Goblin Glider Kits fluctuate a lot. I used to sell mine for around 30-40 gold each about 2 months ago, but recently the market was flooded with them so the price is down to under 10g each on my server. By experience I am pretty certain that the prices will go up again, so right now I am hoarding them on one alt, both by making them myself and by buying them on the AH when they are really cheap. As soon as the price goes back over 20g I will start unloading them for a profit.
The NPC scan and NPC alert method is an awesome way to build a stock of rare BOE items simply because you don't really have to try. By installing NPC scan and NPC alerts, you can literally just fly over anywhere and be alerted when you pass a rare spawn. As we all know, rare spawn loot tends to have higher item vales, as not everyone is able to consistently farm them. Some NPC's, especially those in outlands have those higher item values when compared to the rest of the world. As a goldmaking method I just everyone should be doing this. It only requires you download two addons and you can get access to important NPC,s that you would otherwise never knew existed. The opportunities are endless, I would generally never play without these cool addons. Realy cool.
This farm very much resembles the Dire Maul farm in that it allows you to hit multiple markets without having to do too much. You can mageweave, runecloth, greens, world drops, and herbs all from this one single spot with the addition of countless transmog items. I personally love this spot – however I feel I stumbled upon it a little to late. The benefits is that this is the LARGEST instance in the entire game – literally. You can spend up to 15 minutes pulling the entire instance. You are rewarded however with an abundance of drops of all kinds. You can quickly fill up your inventory here. If you need greens form the 47-51 area, this is your spot. As mentioned, you will also get soo many trade goods that it's hard not to fill even the biggest of bags.
Items you buy from vendors can be resold on the auction house for a profit. The most common way of making gold this way is finding either vendors with limited supply items that you can only buy a set amount of a particular item from and then you have to wait a while before someone can buy more, or buy items from vendors located in locations that are far off. There are also vendors that will sell items for other currencies than gold. One more important thing to note is that you can sell very common easily available items on the AH as well. Like crafting materials from profession supply vendors that only cost a few copper or silver that can be resold on the AH for gold, and they actually have a decent sale rate.
AQ20 is a really nice transmog farm. The worms called Silicate Feeder are actually the mobs with the best loot in the raids so be sure to loot them. They are found between the 3rd and 4th boss. Be sure not to kill ANY of the mobs in the room with the 2nd boss as that will start the encounter for the boss. You can go through the whole instance without killing any bosses, so you can choose to run the entire raid or exit after killing the worms by creating a group in the group finder and leaving it.