One recent eCommerce site client was spending 4 figures a month on ad buys without any degree of monitoring. It was cash flow positive but not at the rate we wanted.
We took two approaches. We first optimized the data and eliminated all under performing campaigns. Then we expanded the campaigns beyond just Google to Bing, Twitter, LinkedIn and continue to expand.
Secondly, we did a grassroots campaign using the data from the ad buys. This allowed us to further increase their yield and growth.