It is quality in every area of your business. At the very least, your product or service has to do what it is supposed to do. Go beyond the minimum and produce at a higher level of quality, wrap quality service around it and you will exceed the customer's expectations. We are expected to provide solutions to problems. If we don't, the customer will go somewhere else.
Complaints are obvious.
Hopefully, this is not an ongoing occurrence. Second, there is the need type of problem. For example, let's say you are in the hotel business. A traveler needs a place to stay for the night and your hotel is the solution to the traveler's need. You solve their problem by having a nice comfortable room that meets, if not exceeds, their expectations.