Integrity means doing what you say you'll do when you say you'll do it. It's the imperative foundation for creating trust.
If you cannot guarantee something for a customer then do not make them a promise.
Provide the best insights, advice and recommendations you can and leave it at that. Making commitments that are questionable will lead to your customers having questions about you, your word and your firm.
If you do happen to make a commitment you cannot keep, let your customer know as soon as possible. Do not wait until the due date/time, it just erodes your credibility further.
Explain why you cannot keep the commitment. If you've built sufficient positive equity with your customer over the course of your relationship, they'll forgive you. Just don't make a habit of it or you'll surely run out of equity.
Never lie to a customer -- it's hard enough to keep up with the truth.
You can never thank a customer too much. Thank them in person, thank them over the phone, via e-mail and especially with a handwritten note. In this day and age, a handwritten thank you note is very powerful.
Find creative ways to thank your customers and show them you appreciate their business. Amazon used to include bookmarks with their books. I thought this was a great value add and advertising vehicle for them but they stopped.
Thank your employees for treating your customers well. They're on the front lines with customers representing your business. Treat your employees the way you want your employees to treat your customers.
A company's commitment to provide outstanding customer service starts with senior management. That level of commitment is reflected by every employee. Zappos is a great example of this.
Ensure that you and your customer's definition of excellent service are congruent. Set or define expectations early in your relationship to minimize confusion as the relationship expands. If you're not sure what your customer's expectations are -- ask them!
A friend of mine, Dr. Ralph James, wrote a book for the construction industry called The Integrity Chain. While Ralph wrote the book for the construction industry it is relevant to any industry. The premise is, without integrity you will have fewer customers and less revenue over the long-term. I could not agree with him more.
Do you and your employees just want to make the sale or do you want customers for life?