The correct option is A only rich customers.
The inference that the salesmen in the shop only pay attention to rich people can be made from three sentences in the passage- the first being that the customer "...had come to the same shop in casual dress that morning and had drawn little attention." but when he had come in good clothes, the salesmen "...who thought him rich and likely to make heavy purchases..." were quick to pay attention to him and give him deferential treatment. On being asked by the manager about his intentions, the young man had replied that he "had come in good clothes only to get a decent treatment, not for buying any textile." Thus, the answer to the given question is option B.