A key principle of service design is that the customer is always right only if it's the right customer for you. But let's say you have decided to go after the atypical customer; one whose business is worth the extra effort. How do you win their business--and keep it?

Trust is the key. Service companies depend on trust even more than companies whose primary focus is products, because a service brand is built on the quality of the customer's experience.

Yet experience is inherently intangible and subjective. You may think a restaurant is elegant; we may think it's over-the-top. You can aggregate and rate service experiences (on Yelp, on hotels.com), but you can't test them for defects the way Consumer Reports does dishwashers.

So how do you design experiences that build trust? No group knows better than people in private wealth management.

Wealth managers deal with customers who are privileged, picky, and often paranoid. "Customers in this business--ultra-high-net-worth individuals and families--are justifiably suspicious of anyone offering a service," says Brooke Harrington, a professor at Copenhagen Business School who has spent the better part of a decade studying private wealth managers and written about them in her book, Capital Without Borders.

To win over such people, "you've got to combine the ability to deliver wonky solutions with emotional intelligence," Harrington says. That's the equation for great service design; customer delight is the product of technical excellence and customer experience.

In the rarefied world of wealth management, that equation includes some unusual variables. It helps to have gone to the right schools or play polo, or at least hang out at matches. But many of the design tricks of the trade offer valuable insights for people who work in more down-to-earth realms.

Here are six lessons that can help you perform better for that special customer, regardless of your business:

1. Know every corner of your business.

Wonky solutions for the super-wealthy are often found in arcane clauses in the world's tax codes and in the knowledge of how to construct legal entities to protect, shelter, or transfer assets from one place or generation to another. Picky customers in every realm expect you to know your stuff--and they have a sharp sense of when you're phoning it in.

So if you don't know, don't fake it. Learn it.

2. Show that you understand the client's world and values.

All customers want service providers that "get" them. That's as true for software developers as it is for money managers. That includes sharing friends and social circles--referrals are the No. 1 source of new clients--and displaying the appropriate discretion.

3. Be prepared to say no.

When clients expect you to be at their beck and call, you can prove your worth by defining for them boundaries they mustn't cross--where their wish is actually contrary to their best interest. "Saying no can build trust, because it can be the ultimate evidence of shared values," Harrington says.

4. Stage-manage the relationship.

One of us was taken into a conference room used for client meetings at a private bank in Geneva, where our host advised us to take a look at the table: "See how it's banged up? Shows that we're frugal."

Sometimes it takes a bit of theater to demonstrate authenticity. What shows your authenticity--what you're really all about?

5. Have a great network--and work it.

Wealth managers are solutions providers, hired not just for their specialized knowledge but because they can orchestrate the services of others, relieving the clients of the burden of creating or managing the network.

To whom can you connect your customers? What additional services do your customers need that you can introduce them to?

6. Be prepared to be tested.

High net worth clients often set up extreme, even wacky tests for the people who serve them. Harrington tells the story of a banker in London received a call asking him to help a client find a bracelet lost in the last two days somewhere in Switzerland. "That's not my job," isn't the right answer, Harrington says: "He sucked it up, tracked down the bracelet, and billed the client."

These aren't tests of loyalty and obeisance, like asking a senior aide to swat a fly. They're chances to show a client not just what you can do but what you're willing to.

Just as every diamond needs a great setting to show off its sparkle and value, even the most brilliant service provider requires a clear value proposition and well-designed processes, systems, and networks to back it up. You have to talk a good game but, as Harrington says, "the ultimate test is, 'Can you make things happen?'"

Making things happen builds the trust that is the glue that makes relationships sticky.