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I would try and find out the reason for the upset, and try to address the problem.
If it is a defective product or a salesperson being unprofessional, I would ask the customer to have a seat, and get the supervisor or manager to handle the problem.
If the cause for the upset is another customer, I would separate them in different sections, and get two supervisors or managers to deal with each of them.
This will help so that neither one of them is left feeling neglected or less important to us.