FWIW, I’ve always found that Eclipse’s advice worked best. When you see that they’re determined to rant and yell, let them blow off the steam and just don’t take it personally.
Absolutely do not give mussar — especially if they have a legitimate grievance (even if it’s not against you personally). Your job as a CSR is to fix your customer’s problem, not lecture them about the proper way to call a call center (although there have been plenty of times that I was sorely tempted to).
The Wolf