The Association of National Advertisers said this month that rebates and nontransparent practices are “pervasive” in the U.S., as evidenced by the outcome of an eight-month probe by corporate research investigations firm K2 Intelligence.

The ANA trade group, which represents big advertisers such as AT&T Inc. and Procter & Gamble Co., concluded that ad companies are being rewarded with rebates from media companies for spending money on behalf of their clients, without the clients’ knowledge.

The report raised alarms for marketers about how their ad agencies conduct their business, but not everyone is convinced by its findings.

Read the full Wall Street Journal article here.