Marketing intelligence relies very heavily upon publicly available information. This can be as easy as talking to customers, or having a poll online that everyone can access. Other places that can be accessed include databases, call centers, and any relevant print media. Print media could include books and newspapers, as well as encyclopedia entries, magazines, posters, and printed ads.
This kind of intelligence makes it easier for companies to market across a wide girth of society. Since the main point of any company is to make money, this would actually make sense as a business strategy. If the information is free to access, why not use it to their advantage? That said, it is harder to stay out of the information collected with the prevalence of the various ways your information can get into the public domain.