Own the value chain
For crafted items where thousands have the recipe, there is often little profit beyond mat value, i.e., it’s not worth buying mats to make the item.
(In fact, there is often negative profit in crafted items, because people have to make them to skill up.)
Sometimes, though, there are pockets of profit in each step. Raw gathered mats have value, and often offer the biggest cut of the profit. Converting these to second-stage mats sometimes yields a small profit (for example, smelting ore into bars – if bars have multiple purposes), or making intermediary mats. Then there is final crafting (blacksmithing, tailoring, leatherworking, jewelcrafting), which can add some value as well.
For many items, profit can move around in its value chain. Often most of the profits are in the mats, but this can change, depending on what people are making, farming, changes Blizz makes to the usefulness of items, etc. If you can perform all steps (even if on different toons), then you own the value chain and can capture the profit wherever it may be in the chain.