The surprising answer is that we don't know. Here's why. We know what customers SAY they do, because almost all the research relies on self-reports and surveys. That's why you'll see all the statistics that say dissatisfied customers tell x number of people, or that angry customers can influence x thousands of people on Twitter.
Talk and Behavior Different When It Comes To Consumer Behavior
If you aren't familiar with Psychology and research methods, you'll probably be surprised to learn that there can be a large gap between what people say and what people do. So, think of it in terms of your own behavior. Have you ever been to a store or restaurant and said: "I'm never going back", or "I'm going to tell all my friends not to go there".? Did you follow through EVERY SINGLE TIME? In fact, did you ever go back because it was convenient, or because the store had something you couldn't get anywhere else?
Most people aren't that consistent. In some cases you might follow through, and in others you might just plain forget, or figure it's not worth the hassle, because you are busy.
There are a lot of reasons why what people say, and what they do often differs, and one is simply that people want to think of themselves as being strong, not taken advantage of and so forth. That bias often affects how people portray themselves in survey data, because even with anonymous surveys people want to appear strong and active TO THEMSELVES.
The implications are exceedingly profound. The "research" is certainly biased towards soliciting information about customer behavior that will be affected by the above bias, so it will OVERESTIMATE the behaviors that can damage companies that provide poor service. Of course there are a lot of depends; Some people will follow through. Some will only follow through at the most aggregious affronts. Others will never do anything. So, before investments in customer service, companies should question the validity of the survey research about consumer behavior that they are acting on.