What kind of clients a photographer is afraid of

Customer is God. As photography is in the service industry, satisfying the customer’s need is our responsibility. However, I really fear this kind of clients: they don’t know what they need exactly. When I asked them to give me sample photos or instructions, they replied: “you can take whatever photos you think the best.” When I created the pictures, they are not happy with the result, but they can not tell me what is the problem about the image. They are just not satisfied. I wonder: if you don’t clearly know your own needs, how can meet your expectations?