K2 Intelligence, the firm behind an explosive report revealing that nontransparent practices are pervasive in the advertising industry, is starting a division dedicated to helping marketers investigate whether their ad agencies have done anything improper.

The corporate investigations firm conducted an eight-month probe into the ad business on behalf of the Association of National Advertisers, a trade group that represents some of the country’s largest advertisers such as Procter & Gamble and General Motors. The June report found that advertising companies are engaging in nontransparent business practices in the U.S., including being rewarded with cash rebates from media companies based on the amount they spent on advertising on behalf of clients. In the case of rebates, advertising clients interviewed for the study weren’t aware of them being returned.

Read the full Wall Street Journal article here.