4 Mistakes Ecommerce Marketers Make When Measuring ROAS

Most ecommerce businesses rely heavily on advertising to draw customers to their websites. When it comes to measuring ad spend, there are a handful of common pitfalls that every ecommerce business must know how to navigate.

In what follows, we list four different mistakes marketing managers are prone to make when assessing the return on their advertising investments (ROAS), and the only ways to avoid them.

Double (or triple) counting a conversion. Often, ecommerce businesses will use different agencies to manage different channels. There is nothing wrong with this unless the measurement is conducted through the use of the engine data of the different platforms.

Google, Facebook and the other platforms are all too happy to claim success for a conversion. In many cases, adding up the data from the different platforms will show up as multiple purchases while in reality there was only one.

It’s only through the use of their CMS systems, or possibly even just their Google Analytics last touch attributions, that businesses will avoid over-counting purchases.

Incorrect growth measurement. An ecommerce business will encounter unexpected swings in sales during a period of time, and so the business will naturally want to know what happened. While it’s helpful to asking questions about irregularities, jumping to conclusions about the effectiveness of a paid advertising campaign because you see a sudden change is far from prudent.



The most mundane reasons can cause spectacular changes in patterns. Take the weather, when a period of cold and rain followed by agreeable weather will have people run to be outside and forget about online purchases for a few days. Does such a scenario indicate a failure of the advertising campaign? No, of course not.

Businesses will do well to focus on year-over-year measurement, comparing one January to the next, if they want to measure the success of their ecommerce marketing successfully.

Wrong measurement design. Another common mistake made in setting up measurement is ignoring the differences between channels.

Google Ads cookies used to expire in 30 days. Most ecommerce marketers got into trouble when Google’s data was compared with the data from other channels. It is important to be able to compare apples to apples—or, when you must compare oranges to apples, to at least know how many apples an orange is worth.

Another mistake pertains to plain errors in setting up the data sets. Google Analytics is very useful for measuring ROAS if, and only if, the team actually knows how to use it.

Listening too much to ad sales reps. Sale reps from social media platforms will often tell businesses that they are “leaving impressions on the table,” and that their bidding is suboptimal, leading to a lower rank than they could potentially have. The fact of the matter is that ranking high is not always what you want to achieve -- because the loss in margin will often not be compensated by the increase in sales volume.
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