Suppose we have standard world of fantasy RPG videogame. The MC (main character) earns money by killing monsters and then selling loot. Also, sometimes there are people happy to pay generous reward for slaughter of especially vicious monster. As an adventurer they aren't a member of any guild.
The MC can also craft artefacts. Some ingredients can be bought, some can be collected (like herbs), some can be stolen, some can be harvested from dead monsters. And then from these ingredients an artefact can be crafted by the MC and then sold. If total cost of ingredients needed for crafting an artefact < market price of the artefact, then the MC willcan get profit. But for some strange reason it is always more profitable for the MC to just sell ingredients at their market price, than to craft an artefact from them and then sell it at market price. Why? Especially considering that there seem to be people in this world who find it more profitable to sell crafted artefacts, rather than sell ingredients needed to craft them (otherwise no new artefacts would be available for sale).
P.S. I'm not a writer, I just encountered this situation in a videogame RPG and wanted to see somehow realistic explanation for such situation. For this reason crafting system of the game doesn't matter.