As a professional speaker, I deliver a speech called “Galvanizing Your Business with Word of Mouth Marketing” to CEOs and entrepreneurs around the country. Without exception, audiences are intrigued by a simple yet powerful concept that I call “the thirteenth cookie.”

Before I go any further, I must confess: I have a sweet tooth. It is rare for me to pass a bakery without popping in for a little treat. Fortunately, Portland has some terrific bakeries (too good, perhaps!). But what really makes me happy is when a bakery unexpectedly throws in a little bit extra. Sure, the “baker’s dozen” is hardly a new or unique concept. But these days, very few bakeries give away anything—thanks to the ever increasing prices of ingredients, insurance, employee wages and more.

Yet I’m hardly alone when I say that an unexpected, complimentary item puts a big smile on my face. It solidifies my goodwill and motivates me to recommend the business to others. I call it “the thirteenth cookie” effect, and it is unbelievably simple. Of course, you don’t literally have to offer a cookie (although DoubleTree’s famous chocolate chip cookie is one way that the hotel chain differentiates itself from its competitors).

You may also find that what you offer is far less important than how it is offered. Last summer, I went to the car wash and the clerk told me that he was going to wash my car for free. Surprised, I asked why and learned that I had washed my car nine times and the company always offered a free tenth wash. Even better, they were tracking my car washes automatically.

Whether it’s the “thirteenth cookie” or the “tenth car wash,” unexpected surprises go a long way toward building customer loyalty and generating positive word of mouth. Maybe that’s why my audience members, both B-to-C and B-to-B, light up when they hear the idea. They leave the presentation with a plan to challenge their own teams to come up with an unexpected product or service that will delight their customers.

What’s your company’s “thirteenth cookie” plan for increasing referrals and building loyalty?