A Chamber of Commerce is a group usually coordinated through the local city that are usually reputable businesses and get together to help "guide" the city's businesses in doing "good" business. There's usually a fee involved and there are certain requirements to be part of it, although it's not an elitist group. Also is used as a networking and advertisement resource, as most fly-by-night companies won't join. I'd probably trust a chamber member more than just some random yellow-pages ad.