If you want to get and continuously stay rich in WoW there’s one defining factor that has been true since the dawn of the game. You need to blaze your own trail!
Popularized methods are lower profit
If everyone knows about a method, then the profit will go down. The less competition you have, the more gold you can make. Obviously this makes it a bad deal to share all your secrets on youtube or on your website. The obvious advantage is that you can make real life money that way. People who truly care about getting reach will keep their methods under wraps for a while. Kaychak for instance has noticed that his videos generally tanks his markets, and he likes to keep his best methods under wraps when new expansions roll around.
You need to find the best methods yourself
The only way to find the best goldmaking methods in the game is to find them yourself. You need to look at prices, test professions on the PTR and put in the effort to get ahead of your competition whenever possible. Throughout WoWs life and various patches the methods for large scale goldmaking have varied greatly. The same is true for how easy it is to find the best methods. Sometimes they are also hard to unlock, which creates the perfect storm for making multiple gold caps.
How do you find the methods
There are some evergreen markets that always work and always have. Cosmetic flipping is a stable method, and the general approach hasn’t changed much, but it is VERY difficult to generate extreme amounts of sales in a short amount of time. To do that you HAVE to target items that make characters powerful. Gear, consumables and enchants for max level characters. WoW is a game about improving your character so that is what players spend by far the most gold on.
Bis lists
Wowhead guides, class discords and similar places are extremely important. This is where players find the items that will have the largest impact on performance, and thus the largest market. These are the recipes you want to get and the items you want to target.
Testing
The other side of the research coin is finding the best way to craft items. This includes getting the required recipe and skill, as well as the right build in the War Within. To find the hidden gems you need to do your own testing to find optimal skill builds and proc rates of random processes like prospecting to get the data. It will eventually be available, but by then someone will likely have already made millions.