Stalking the halls of offices across the globe, tying up phone lines, and blowing up email accounts is a menace known to businesses large and small: the nightmare client. While they may be energy leaches, these customers also hold a valuable secret. In the words of Bill Gates, “your most unhappy customers are your greatest source of learning.”

There are many reasons lurking beneath the behavior of these clients. While you can neither know nor control all the variables, you do have a choice in how you respond to them. Choose wisely, and you’ll boost your business, confidence, and emotional intelligence all at once. Read on to discover just how to achieve this seemingly impossible feat.

1. Be Generous

While thoughtful corporate gifts, perks or fancy lunches may appease your troublesome client in the short-term, true generosity goes beyond that. One of the most powerful things you can give is your time. This is probably the last thing you want to do, but allowing them to voice their needs, wants, grievances, and concerns will allow you to create an informed plan for your future dealings with them. Getting on the same page is the first and most important step in winning their trust and coaxing them out of the “difficult client” category.

2. Stick To What They Need

Most customers have had to deal with so many pushy salespeople in their time that even a hint of upselling or sales jargon will have them assuming you’re just after their money. While you may believe the extra products will help the client out, if they’re difficult or untrusting, you may just end up aggravating them.

In these cases, it’s worth focusing only on what they need, and holding off on other pitches until you’ve developed a greater rapport. By all means, lay all the options on the table. However, an honest assessment of what the client actually needs right now, even if that means fewer dollars today, will convince them that you have their best interests at heart and help win their trust. Once you’ve achieved this, especially if they were difficult at first, they will often upsell themselves in the future.

3. Under-Promise and Over-Deliver

You’re certain to have heard this one before, but it’s worth repeating because it’s surprising how many people know the rule but fail to implement it: Telling people what they want to hear and agreeing to their requests and demands can feel like the right thing in the moment, particularly if it’s a difficult client you’re dealing with. However, when you acquiesce, you rob your future self of the rewards of underpromising and instead invest in a mountain of stress.

While clients may not be happy if you tell them a deadline isn’t realistic or that next-day shipping is unlikely, they’ll be content when you meet the realistic expectation you set. And here’s the bonus: if you make their initial request happen, you’re not just doing your job, you’re a hero.

4. Reframe Your Apologies

While you should always be honest about mistakes you’ve made, keeping the s-word out of the equation will serve you well. Instead of: “I’m so sorry, I promise it won’t happen again.” Try: “I understand how frustrated you must be. I’m aware of the impact this will have on your business and so have made resolving it my top priority. Thank you so much for your understanding and patience.”

While the mind of a difficult client is a swirling enigma you should never attempt to comprehend, there’s always a way to settle the tension. Follow the above steps and you’ll never have to look at an incoming work call with dread in your heart again.