That big customer is angry and ready to bolt. What now?
Leigh Thompson, professor of dispute resolution at Northwestern University’s Kellogg School of Management, says you’ll have a better chance of keeping angry customers if you:

• Let them vent. People want to be heard. Letting them blow off steam doesn’t mean you agree with them. It just means you’re listening. Check to make sure you understand by summarizing what the person is saying.
• Apologize if you’re wrong or made a mistake. If you failed to do something you wished you’d done, say so. Make sure the other person hears your apology loud and clear.
• Don’t take it personally or get hung up on tactics, no matter how offensive the customer becomes. Try to exercise patience. Cooperation works better than competition in negotiations.
• Focus on the issues, not the personality of the customer. What can you do to make sure this misunderstanding doesn’t happen again? Both sides in a negotiation will often have a problem which the other side can help solve. But before the solutions flow, the climate has to be right – problem-solving has to be a two-way street. This can be done and is done every day: two parties working closely together to find better ways to strike a bargain for the advantage of both.