In general, my experience has been that the WoW market for crafted items is efficient enough that it's hard to make much profit through crafting; the market price of the raw materials is about equal to that of the finished product. The exception to this is with uncommon recipes, for which there's an economic impact of having the recipe. (Though then, the price of the recipe skyrockets to the point that it will take ages to recover the cost.)
But: Roktazza learned the pattern for the Big Bronze Knife from the trainer, at a blacksmithing skill of 100. (This is a pretty low skill, and the fact that it's from a trainer means that it's widely available. Almost every blacksmith can make these.) She can buy the materials for this for 30 silver or less in the auction house, and then sell the knife for 82s, for a profit of about 50s per knife. And this isn't a one-time thing; she's sold about 20-25 of these knives, and has often sold five of them in a day. (It takes enough time to sell through that I'm not sure she could sell much more than that, though.)
I can understand why people might want to buy these; most classes can use daggers, and stamina is at least a decent stat for every class. But I don't understand why other suppliers aren't crowding into the market and driving the price down until it's barely profitable.
It's nice to have 20 gold at level 18, though. And it's nice to have my Blacksmithing skill up to the level that I can make any crafted item that I can wear.