If a person or organization is disreputable, they have an image problem. They are — or at least appear to be — crooked, shady, or just plain bad news.
See how the word reputation is partially hidden in disreputable? If a person is disreputable, they have a bad reputation for some reason. A student caught cheating will get a bad reputation with teachers and become disreputable. A politician caught in a scandal could become disreputable. If an airline crashes a plane, they will become disreputable. When someone or something is disreputable, people no longer trust them. Even if the reality is different, it's hard to shake off a disreputable image.