In World of Warcraft, you basically make money out of people who are lazy. Or stupid. But mainly lazy.
Okay, here’s an example. In the game, I have Enchanting as one of my professions; basically, given the right set of ingredients, I can bestow certain enhancements on weapons and armour which improve them in certain ways – and, more importantly, make them glow cool colours. To get the ingredients, you have to “disenchant” fairly rare to incredibly rare items, with the “power” of the enchanting ingredient increasing with the rareness of the item.
Also in WoW, there’s an Auction House for people to sell items in – anything you can pick up is tradeable, basically, for whatever people will pay for it. So, these fairly-to-incredibly-rare items show up on the auction house more often than they get dropped by enemy characters, and so is where most people get them from.
Now here’s the thing: If I buy a fairly-rare item off the auction house, disenchant it into enchanting ingredients and then put those ingredients back on the auction house, they will sell for more than the original item. The only people who can use those ingredients are other Enchanters – i.e., those who could have bought the original item in the first place and disenchanted it themselves. So I can make stacks of cash buying cheap, low-level rare items, disenchanting them and selling the resulting ingredients back to people who could have just done exactly the same thing themselves.
People are lazy. Stupid, too, but mainly lazy.