A scam site is a website that purports to reveal the truth about woo-based scams and fraudulent products but on closer inspection are in fact filled with fake testimonials and anecdotal evidence that supports the product in question.
Scam sites are an extension of the search engine optimization (SEO) employed by companies to boost their web presence. In the case of fraudulent products, it is likely that suspicious people will immediately go to Google and type in something along the lines of "Woo Product X scam" or "Woo Product X fraud" to try and find information about whether a product is genuine. By registering domain names featuring terms such as scam and fraud, companies can drown out criticism of their products with false praise.
This tactic isn't restricted to fraudulent products but has also appeared in a more sinister guise with hoax viruses. In some cases virus hoaxes are circulated, via Facebook for example, and malicious sites that host actual viruses immediately spring up to capitalize on the relevant search terms.