Disgruntled customers used to have little recourse against poor service and broken promises.

But as angry clients increasingly turn to the Internet to settle scores, companies, independent retailers and everyday wrongdoers are learning that consumers can have the last word — and often, the last laugh. On the Web, shame and humiliation are sometimes the strong-est weapons in fighting scams and unfairness.

AOL got burned last week, for example, when an exasperated customer recorded and broadcast online a service representative's emphatic reluctance to cancel his service. Comcast Corp. fired a technician after a videotape purporting to show him asleep on a customer's couch became popular on sites such as amateur video site YouTube.

People are also using the Internet to retaliate against common thieves and discourtesies. A popular blog recently posted voice-mails from a man demanding that his date pay him back for half the dinner check after the romance fizzled. In June, a New York man posted pictures online of a young woman who allegedly refused to return his friend's T-Mobile Sidekick that had been taken from a taxicab; the Web site became popular among other victims of cell-phone theft, leading to her arrest.

And there was the South Korean woman who was humiliated last year when she didn't clean up the mess her dog left in the subway after a fellow train rider posted a photo of the incident on a popular Web site.

"There's no question that publicly shaming someone, whether it is a politician or a company, is the best way not only to get their attention but to change their behavior," said Jeff Chester, executive director for Washington-based consumer advocacy group Center for Digital Democracy. "People are going to be very sensitive to it."

Online disgrace creates so much buzz on blogs and in the media that companies are beginning to realize the devastating public relations effects brought on by these grass-roots exposes, said Gemma Puglisi, assistant professor of communications at American University.

"This has been a wake-up call for these companies," she said. "The day where you send a little letter to the CEO is over. In the age of technology, you have to be even more careful of how you treat your customers because you don't know where they're going to go. Now everything's out in the open."

The Internet has long been a forum for rants about unsatisfactory service and faulty products. Just about every major retailer has a consumer-created counter-site that lists complaints, and dozens of all-purpose sites allow people to share their opinions on everything from apartment complexes to car dealers.

"I think the inherent nature of the Internet brings out the inner complainer in us," said Joe Ridout, a spokesman for Consumer Action, a San Francisco advocacy group. "To get back at people who are out to steal or swindle, shaming may be a reasonable response."

Some customer service representatives are fighting back by starting their own sites to complain about annoying customers. Such sites also are useful in showing a company's true character, Ridout said.

"Anything that produces more information, anything that penetrates this slickly manicured image, is useful information," he said.

The rise of user-generated commercials gives angry consumers yet another opportunity to get their message on the Internet.

In March, Chevrolet added a feature on its Web site that allowed visitors to piece together images and text to create an ad for its Tahoe sport-utility vehicle. But anti-SUV activists used the site to make a negative commercial condemning the vehicle for harming the environment.

Such watchdog-type content has "become invaluable as a way of checking on firms, as well as countering them," Chester said.

But the well-oiled marketing machines of the targeted companies will overcome the negative publicity in the long run, he said.

"As the Internet becomes more ad-supported, it's questionable if consumers and users will have any real clout," he said. "Will a Fortune 500 company hear the sound of one angry blogger in the digital forest?"