If you find postings in newsgroups, read all the messages about the subject and determine if you need to respond. In some cases, the issue dies, or smarter minds call the poster to verify his information. Newsgroup netiquette forbids advertising in newsgroups, but not the honest exchange of information. Contact the original poster directly and see if you can work out the problem. Maybe there was some miscommunication that went haywire.
Many people are reasonable.
In fact, some of the biggest fans for companies were once people who had customer service problems that were set straight. Before you call or write, see if the person posted other messages in other newsgroups. Dejanews provides links to all messages the person posted. That case would require a different strategy than if he belonged to professional scientific organizations. If you find a rogue Web site, see if you can talk to the Webmaster and find out what the problem is.