When we think about companies in which we might invest, we tend to think about business models, growth rates, and profit margins. We think about the CEO and debt levels, and recent news. That's all good. But we shouldn't overlook a key factor that can be a powerful competitive advantage: customer service.

If a company has or is known for poor customer service, that can hurt it. Recall how we're often reminded that someone who has a bad experience will tell lots of people about it. Well, they'll tell people about good experiences, too.

The folks at Forrester Research recently surveyed more than 4,500 people about their experiences with companies. They found that consumers tell more people about a bad experience than about a good one. In a separate study, Forrester found that good customer experiences create loyalty and turn customers into referral sources for future business. Interestingly, this latter survey, reported in 2009, also found that this phenomenon was stronger than it was last year, suggesting that good customer service is growing in importance.

Potential losers from poor service
This spells trouble for those companies with poor service. Which firms are those? Well, MSN Money recently unveiled its "Customer Service Hall of Shame," a few members of which I've put below. I've also included their stock returns over the last year and their star rating from our Motley Fool CAPS community to give you an idea of how attractive our members think each company is.

Company

CAPS Star Rating (out of 5)

1-Year Return

Comcast (Nasdaq: CMCSA)

**

(27.0%)

Sprint Nextel (NYSE: S)

**

(48.0%)

Capital One Financial (NYSE: COF)

*

(44.9%)

Abercrombie & Fitch (NYSE: ANF)

**

(56.2%)

Hmm ... clearly, these are not among the most attractive stocks right now to Foolish investors, especially given their weak returns lately.

What makes a winner
On the other hand, here are some companies that earned good marks for customer service:

Company

CAPS Star Rating (out of 5) Continued...