There's a lot of big differences--anyone in the real world who can get the drugs can sell drugs, and the illicit nature raises prices, plus no Divinations in our world. In Eberron, the number of those with True Dragonmarks is low, and the Houses pretty much know who all of them are--plus, we're talking about openly undercutting. Doing a few for your buddies surreptitiously (within an adventure)? Sure. Opening up a storefront thread and making thousands of gold identifying infinite items out of adventure? That shouldn't fly.