From my experience in finance (where being yelled at is unfortunately quiet common)..
First step is body language. Listening attentively to clients complaint without interrupting. Nodding where appropriate and maintaining eye contact.
Next is paraphrasing the clients complaint to show you heard what they said and understand. Important to do so without actually saying you understand. For example "I can hear that you are really disappointed in your cut as you specifically requested blah."
Next ask the client what outcome they would like. Do not just offer a refund, as this may not be what they want, and you are letting them leave without resolving the issue. If their request is reasonable - go ahead and do it! If you can't accommodate their request explain what you are able to do. Emphasis on what you can do rather than what you can't.
Only one person should be involved in resolving the complaint so client does not feel intimidated or ganged up on. Managers should stand back even when listening until invited to join discussion. Whoever handles complaint should do so with confidence so client is reassured they can handle situation.
Always remain respectful, never engage in an argument. However there does need to be boundaries for staff safety. Customers that become overly aggressive or violent should be informed immediately that the police are being contacted and that they are required to leave the premises.
If you successfully resolve a complaint for a client and have them leave satisfied they are much more likely to advocate for your business, even more so then if they had gotten the correct service initially (weird). I would call that a definite positive.
I would also recommend followup call from management for serious complaints.
Long winded but hope that helps!