There are two related ways that a firm can do this.
First, a firm can look at blogs that have been written about it. It can look at those blogs to find out what customers think it is doing right and what it is doing wrong. Using that feedback, the firm can try to remedy the things that it is doing wrong and emphasize and further strengthen the things it is doing right.
Second, a firm can look at blogs about other similar businesses. It can look at the feedback that is being given to those businesses. It can use that feedback as well to try to determine what it is that customers look for in terms of products and services.