Practise your skills in assertive communication. Find a friend or fellow learner who will pretend to be a dissatisfied customer. Plan the sorts of phrases you can use to clarify the problem, empathise, and deal with the complaint effectively whilst not losing sight of the importance of maintaining your business standards.

You may even find it useful to film the interaction so you can compare what actually happens with what you thought you said.

You may be surprised by your communication skills.

It takes a lot of practice to say the right things in a situation where someone is dissatisfied and may attack you verbally.

Good luck with developing good customer service skills.