As marketers push for greater transparency in how the murky world of digital ad buying works, agencies are rethinking their approach.

For the past several years, as automated ad buying has taken flight, agencies have made a lucrative business out of running an arbitrage-based model — buying digital inventory in bulk and then marking it up for advertisers. The clients didn’t cry foul, because they were happy with the performance of digital campaigns or because they weren’t clued into the complexities of digital ad buying and agency profitability.

Read the full Wall Street Journal article here.