Generally speaking you can get paid by other people if you provide something that’s valuable to them. This is of course also true in World of warcraft. So let’s look at some of the main ways value is created in WoW.
What is valuable?
Before we can look at how value is created we have to have an idea of what value is in a WoW context. As I have said again and again I think WoW primarily is a game about improving your character. So anything that improves your character will be viewed as valuable. The more powerful something is, and the easier it is to start utilizing it the more expensive it is. So the most expensive items in an expansion are usually high end gear.
Farming
The main value in WoW will always be created by generating items. There are tons of different sources and all of these provide value. This is of course why farming works. The way you provide value here is of course by venturing out into the world and generating new items from nothing. This is the most basic goldmaking method and it is of course extremely wide spread.
The value you generate is of course the power of the item. The rarer it is the more valuable it will be, and this also holds true for how difficult it is to acquire. Gear from raids is always more expensive than something that can be AoE farmed.
Crafting
Crafting is used to generate items that can only be generated by crafting. When you craft something you need to get the recipe, level the profession and assemble the required materials. All of this requires some amount of playing the game, and without you the item you created would not exist. In some ways the value you create is very similar to gathering or farming as you create an item, but it’s not created from nothing. You turn something semi-useful into something that’s very useful.
All of this requires time, risk and gold and you can usually get pretty nice gold per hour from doing this as a result. It’s annoying or boring for a lot of players so they are willing to pay to just get their items. Rarer, more expensive recipes alongside of how powerful the item is will determing how much perceived value you generate and the profit you can expect.
Services
Services is another extremely profitable way of making gold. Here you help players achieve their in-game goals directly. Whether you are selling m+ boosts, leveling boosts or mythic raids players get access to cool stuff they otherwise would have had no chance of getting ( or at least a significantly harder time getting).
Flipping?
You can make the argument that flipping does not provide much value. For stuff like BoE flipping where you rely on someone mispricing a single item you could even be right. What you are providing is liquidity. You ensure players can more easily sell items they want to sell, for reasonable prices, and you ensure items are more often available at reasonable, but slightly higher prices. For high volume items like materials you help even out the number available. Of course this does not actually create new items or give other tangible benefits, so you are purely playing the economy here. If you don’t want to get up close and personal or competitive, you can just stick to crafting or services where you always generate value in terms of items.