"Companies rely on billing specialists to develop and send bills and collect payments from customers for services rendered. Employers are looking for candidates with familiarity of basic financial software programs and the strong communication skills necessary in an administrative setting. No degree is necessary for this position, but an associate's degree in accounting or a related field will give you a leg up."
What has been your past experience with difficult people?
Remain calm and try to gauge the situation, always pointing out you're willing to help but not to the point where you jeopardize your other tasks. If they prove to be too difficult, then seek advice from higher.