One way you can take advantage of this is by identifying things that have intrinsic value that they're farming for. They have little to no vendor value, and when a botter crashes the market, unless you're one of those masochistic glyph sellers who have the ability to actually mill and use thousands of stacks of herbs, you don't want to buy the herbs for resale for wow gold. For example, Saronite Ore can be smelted and vendored for 12.5g a stack. When you see it at 9g a stack, you know that you are safe buying as much as you are willing to smelt with no risk.
Don't make that assumption for herbs, though. Why are these prices fluctuating so wildly about buying wow gold online? Additionally, there can be demand spikes. The number of people looking for a new meta gem will depend on the RNG of all the raids that night. Overall it will be pretty well averaged out, however there certainly are nights where more people got helms than usual.
You take a risk by buying product for resale wow gold. In the real world, this function is somewhat similar to a "market maker." Market timing price speculators are contributing to market liquidity -- there's more demand on off nights, and more supply on busy nights. This is not cheating, nor is it a bad thing. People who say that you're controlling the markets fail to notice that you're also helping level out supply. This is a good thing for your average player, not a bad thing about making wow gold.