A dead give-away that a guy has zero fashion sense and is not style savvy is that he's wearing the wrong belt with the given outfits. Aaron Marino of alpha m. discusses the two options: casual and dress.
A simple rule to determine whether a belt is casual or dress is by using your thumb. If the belt is about as wide as your thumb, it's a dress belt. If the belt is wider than the first knuckle? It's a casual belt. The belt should match the shoes. For example, dress shoes with high shine get a dress belt with high shine. It's that simple: the thumb tells if it's a dress or casual belt, and the shoes tell you which one to wear it with.