Over the past decade the advertising business has been going through structural upheavals rather similar to those that have been seen in the financial services industry, with the emergence of both giant multiservice global agencies and specialist boutique suppliers of specialised services. These changes, along with growing centralisation of media ownership, have compounded principal-agent problems that had long complicated the operations of the industry. But they have also brought new means for the advertisers to get round them. The paper explores scope for opportunistic exploitation of information advantages in this industry and the checks and balances that may serve to counter such behaviour.