The reputation of a company controls its profit margins. A bad reputation means fewer customers. If you cannot handle difficult customers, that would be a major obstacle for you in a job where dealing with irritated members of the public will be routine. Start generally but select one incident soon afterwards and describe the outcome of that. Be very clear about the circumstance what happened and how you dealt with it, especially how you resolved any tricky issues that arose. The key words here are mutual respect, listening to the customer, being calm in the face of irritation and concluding the situation positively.