It happens all the time: The hard-working crew at a small business loses customers thanks to the sour grapes of one person.

It could be a disgruntled employee, an angry customer or even a competitor, says V. Michael Santoro, coauthor with John S. Rizzo of Niche Dominance: Creating Order out of Your Digital Marketing Chaos.

“Anyone can post a bad review online and hurt your business,” says Santoro, who is a managing partner with Rizzo of Globe On-Demand, an internet technology company. “Unfortunately, most business owners are not even aware that these bad reviews are out there.”