There are multiple methodologies available for handling an unhappy client. First, determine if the client is amenable to discussing the situation. From there, determine the true sources of the unhappiness. Sometimes a client may be disgruntled for external reasons aside from you and your company or its products and services. See what you can do to make it right, even if it is not truly your problem. You want to keep the customer and also gain a new friend, sincerely. Map out the issues on a notepad or on screen. Talk through these matters with the client. Avoid making promises that you can't keep, but assure the client you will do everything that you can to make it right. One unhappy client was foisted onto me when I was the freakin' new guy (FNG). I had just learned a few weeks earlier about active listening and asking open-ended questions. The true problem was that the government was going to force the client to spend thousands of dollars he didn't have. His choices were; either close the business or drastically change the business operating model. I listened and discovered his wife had cancer and would die within two to six months. We talked and bonded. By the time I returned to the office, the client had already called and praised me, requesting that only I handle his account going forward. In other settings when the client is unhappy with what our company has done, they are usually fixable this side of a law suit. Get with the client, make it right. Even if the client rejects you, at least you know at the end of the day that you did all you could to make it right.