Well, you have every right to sell a Medium course. You've been here for a long time, you know better than anyone how things function around here, and you've written more articles than most people read in their lives. Even if you were a newbie and didn't have any writing experience, you would still have the right to sell anything that's legal. Whether people should buy the things you sell, that's another question. Some people do need guidance and courses to move forward with whatever they're doing, others can find everything they need online at no cost provided they know how to do some reverse engineering and sift through the details.