I remember a simple tactic that I used in the WoW AH to make some money:
1) Buy bulk of item X.
2) Divide item X into single units and post on AH with a markup in the price.
People would then buy it because they would need only 1 or 2 of X instead of 10. It only worked for some items and under the right market conditions, but when it worked, it was a simple way to make money. From this I learned some important lessons:
1) Convenience == profit. This is the basis of a lot of business and industry. Why do people use and pay netflix instead of downloading shows? Convenience. Why do supermarkets exist? Convenience. And this is just a specific form of a more general rule, time == money. If you can save people time (convenience) then they will pay you for that service.
2) It made me appreciate and respect more how difficult this must be in the real world. In the WoW AH, I don't have to worry about things decaying or transportation or other things. But the supermarket down the street with shelves full of food? How do they know how much to buy in bulk and sell in units before the food expires? What do they do if they're wrong? I realized that just managing the inventory at a store could be an interesting computer problem. Models, simulations, even some AI could be used to try to figure out the best decisions. And companies already do this and those that do it well have a massive competitive advantage.