You should understand that quite a large percentage of the American public cannot write well. Writing well is far more difficult than conversing well because, in conversation, tone of voice, emphasis, hand gestures, and opportunities for questions facilitate mutual understanding.
Obviously, the sentence as written is nonsense: a complaining customer is not a customer who has been kept satisfied. It does not mean that the writer is an idiot; it merely mean that the writer has no clue how to write competently.
The intended meaning might be
Which sectors have the highest rates of complaining customers?
Which sectors have the lowest rate of resolving complaints to the complaining customer's satisfaction?
Both are meaningful questions, but they are quite different questions.
It is also possible that the writer may have intended a compound thought such as
Which sectors have a high rate of complaints and a low rate of resolving those complaints to the complaining customer's satisfaction?
When you question such writers, they say "But you knew what I meant" on the grounds that you should be clairvoyant and that they do not need to make their meaning clear.