1) Overly sweet frosting - Need I explain more?!
2) Too much frosting - I know a lot of bakeries charge close to $4-5 for a piece of this sweet treat. In order to make their customer to think they spent their money wisely, they just pipe the frosting as tall as they could to make the cupcake looks bigger. Balance is the key, OK?!
3) Cupcake got burn on the bottom of the "cupcake top" - and this is one of the main one among all 3. A lot of bakeries they over pour the batter into the pan. When the cupcakes baked in the oven, they rise and the "cupcake top" (you know what muffin top is, cupcake top is the same thing) got burnt a little on the side and the bottom. You might not notice and question what I am talking about, check the pictures below and you will get what I mean (PS. I didn't make the cupcake in the picture=p).