The caller from my credit card provider was effusively friendly. He wanted to tell me about some new service offerings. "Put them in writing and send them to me and I will have a look at them," I said.

"We're not putting anything in writing," he replied.

"Well, it isn't really convenient to discuss it now, I said. "Thank you for your time," he responded, the edge of menace in his voice suggesting he was anything but thankful.

The experience, as so often these days, left me feeling bruised: the call at home, the irritation when I said I did not want the intrusion and, above all, the sense that whatever the encounter was about, it was not about customer service. Why couldn't I have the information in writing, or online, or not at all, if I preferred?

Whenever I write about deteriorating customer service, I receive emails from around the world agreeing with me. Many people sense that something has changed between companies and their customers in recent months. Previously congenial relations seem to have turned hostile.

Have they, in fact? "The short answer is 'yes'," says Johanna Waterous, a director in the London office of McKinsey, the management consultant, and the head of its consumer practice. It is not hard to see why. Companies' profit margins are under pressure and many have cut back on expenditure, whether on advertising and marketing, or on training people.

When you stop investing in training, Ms Waterous says, customer service starts to slip. The deterioration is even greater when it comes to employees with high levels of skill and knowledge. They are expensive to train and hard to replace if you make them redundant.

Even if you can win those people back, upgrading their customer relations skills takes time. It is not, Ms Waterous says, like advertising and promotion, where expenditure can be turned on and off.

In companies that serve other businesses rather than retail customers, it is even more important to continue to invest in employees' skills. Business customers are more knowledgeable so the employees who serve them need to be more knowledgeable, too.

The problem for companies cutting back on staff and on training is that customers, both in the business-to-business and retailing fields, have never been as well-informed. The internet means they can compare prices. In the US, as many as 60 per cent of car buyers use the internet to research prices and models before they buy.

The internet also allows customers to look at what other consumers say about companies' service and to add their own insulting comments. People have always complained to their neighbours and friends about poor service. Now they can tell the entire world, and do it within seconds.

What can be done? Do companies have any choice about cutting investment in employees when times are tough? Ms Waterous insists there is an alternative: to invest in making employees more productive. She says this is what companies such as Wal-Mart and Tesco, the leading UK retailer, do.

The difficulty is that many consumers no longer believe companies are on their side. This is part of a general fall in trust in business, made worse by corporate scandals in the US and the current uproar over chief executive pay. In an opinion poll last year, nearly 70 per cent of Americans agreed with the statement: "I don't know whom to trust any more."

Glen Urban, professor at the MIT Sloan school of management, says, however, that this presents savvy companies with an opportunity. "Although trust in society and corporations seems to be at an all-time low, now is a good time for businesses to embark on a trust-based marketing strategy," he says in a recent paper. *

As when any desired product is in short supply, companies that can provide it can thrive and charge a premium. But, as Prof Urban says, trust-based marketing means more than putting advertisements on television saying "trust us".

What does it involve? "It is an approach to marketing that shifts and deepens the relationship between a company and its customers. Rather than bombarding passive customers, a trust-based strategy creates a positive relationship with an increasingly loyal customer base," Prof Urban says.

How should companies set about building trust? First, he says, companies need to become more transparent to their customers. They must provide channels where companies can track their orders and take up any service problems. "Transparency is not optional, in that customers and third parties will act to expose a company's underperformance. Whether the company admits it or not, the data is out there," Prof Urban says.

Second, companies must be on the customers' side. This means suggesting they go elsewhere if the company cannot provide them with the right products or services.

"Honesty is the best policy when there is a risk that dishonesty will be revealed - and increasing customer power means that risk is unavoidable," says Prof Urban. Giving the sales people financial incentives that encourage them to sell, no matter what, can cause great long-term damage. Third, companies should help customers help themselves. Many customers do not like being intruded on. (I, as I have said, am one of them.) Some like having their hands held; a growing number merely want the facilities to get on with it. The internet makes this far easier; a well-designed website, one that works for the customer, can both cut costs and improve service. Companies can also use these facilities to learn from their customers. Their feedback is a vital source of information for the company.

Above all, Prof Urban says, trust must pervade the company. It cannot be something that the organisation attempts to graft on to its existing structure. Trust may seem, at first sight, to be the responsibility of the marketing, sales and advertising departments.

"But, in reality, creating a trust-based strategy requires more pervasive changes that reach across the organisation," Prof Urban says.

"This trust-generating culture extends beyond engendering trust from customers to include earning the trust of employees and stockholders," he adds. "High ethical standards and open, honest communication with all stakeholders is the corollary of a customer trust-based strategy." Are customers prepared to pay more for products and services that they trust? The John F. Kennedy School of Government at Harvard University last year attempted to answer this question, looking at eBay, the internet auction site. eBay gives sellers ratings, based on buyers' experience of their reliability.

The researchers worked with a veteran eBay auctioneer, getting him to sell vintage postcards over eBay using his own highly-rated reputation and under the identity of newcomers with no established reputation. The highly-rated auctioneer was able to sell his postcards for 7.6 per cent more, they said in a research paper last year.**

Customers are better informed than ever. But they are also busier. Show them you can be trusted and they will pay more and tell everyone else, and come back. In a highly competitive market, many managers believe their margins are already so tight, there is nothing to spare for staff training or making that extra effort with customers. The Harvard research indicates that companies that make the effort have higher margins.

*The Trust Imperative - http://papers.ssrn.com/sol3/papers.cfm?abstractid=40042   

**The Value of Reputation on eBay: a Controlled Experiment. http://ksgnotes1.harvard.edu/research/wpaper.nsf