...This really works and is too easy.
Does this mean that you're happy or not happy, then? Note, depending upon how you're buying your ingredients, you may also be inadvertently affecting your mercantile skills in the same way you are your alchemy skills. Each successful transaction improves a merchant's disposition and improves mercantile skill. It's easy to confirm just be checking the relevant skills progress bar (hover your mouse over the skill) and looking at the change from one time to the next.
Like the previous poster noted, you're leaning to the dark side of the Force
In my games, my char does not sell home-made potions; they're used only for consumption or for training and disposal. And I'm trying not to abuse the merchants. Outside of the game, I know which merchants restock the basic ingredients I use all the time. Inside the game, I now try to acquire those ingredients by gathering and build up a merchant's stock rather than doing a sequence of buying/reselling. At least to me that feels like I'm keeping in the spirit of the game rather than wholeheartedly abusing it.