A necessity, a challenge, the industry's current obsession. Attribution has long been a point of fixation for digital marketing, and commerce media is inheriting this problem.

Over the past few years, the industry has attempted to address this using metrics that are great for measuring activity, but reveal next to nothing about impact. Clicks, views, and ROAS can answer whether someone clicked or converted, but fall short of capturing the reason why advertising exists in the first place: to influence what someone buys.

As the landscape matures, brands, retailers, and commerce partners are coming to terms with the fact that conventional metrics can only reveal so much about the shopper journey — a journey that’s only getting more complicated with the rise of AI adoption and signal loss.

So, if the path to purchase is fragmented and hard to reconstruct, is the best way forward to place more importance on the post-transaction experience?

TL;DR: Jump to what you need

• Metrics need to catch up with the fragmented shopper journey and rise of signal loss, which is making it increasingly difficult to connect exposure with purchase behavior
• Post-transaction measurement gives retailers, brands, and commerce partners the ability to link ad exposure to actual actions undertaken by a customer, giving them greater insight into campaign effectiveness, not just activity
• Incrementality testing, used alongside conventional metrics, is essential for proving whether advertising efforts generate net new revenue, and aren’t simply capitalizing on sales that would have happened anyway

The Journey to Better Insights

A lack of data has never been the issue for commerce media.

Every day, retailers, brands, and platforms generate vast amounts of consumer information. The problem lies in interpreting and understanding this information in a way that accurately reflects the rapidly changing shopper journey.

Far from linear, the average household shops 11 channels for FMCG products, ranging from social media and AI search to websites, CTV, and in-store. Shoppers switch between devices, revisit products multiple times, and make purchases days or even weeks after initial ad exposure, all of which creates an environment where correctly attributing a sale to a single touchpoint becomes extremely difficult.

Not to mention that the identifiers used to stitch together that journey are disappearing. Cookie deprecation, mobile ad-ID restrictions, and tightening privacy rules are shrinking signals at exactly the moment the journey is getting harder to trace. Attribution isn’t just difficult now – it's difficult, and it’s getting harder, faster.

This is significant, given that 50% of advertisers say improved measurement would unlock incremental investment. Yet, many traditional measurement models focus solely on the moments closest to conversion, ignoring the bigger picture.

Conventional metrics aren’t wrong; they’re just incomplete. They capture a real but only partial set of outcomes and were built to reward fast, single-touch decisions. The trouble is that most shoppers simply don't buy that way anymore. This mismatch, not lack of effort, is why attribution is considered the industry’s greatest challenge.

Unlocking the Power of Post-Transaction

Other advertising methods, such as programmatic, often identify audiences based on likely interest. Post-transaction starts with a confirmed transaction, not a guess. It delivers relevant offers, recommendations, or ads immediately after a customer completes a purchase, whether online or in-store.

By doing this, brands and retailers have the opportunity to tap into a high-trust, high-intent moment, which often drives better results. For example, we’ve seen post-transaction placements deliver a 2.5% click-through rate (CTR) compared to 0.25% CTR, which is typical of traditional display ads.

It also means ad spend isn’t being allocated to consumers who are being targeted because they searched for a product or were a demographic fit, and may or may not be interested. Post-transaction means there’s a consistent, consented identity layer connecting each touchpoint.

Ultimately, post-purchase data comes from demonstrated behavior — not assumptions. It's only as strong as the identity match connecting exposure to that purchase. But when that link holds, it's the closest thing to ground truth commerce media has.

Commerce Media’s Missing Metric

What really sets post-transaction measurement apart from conventional metrics is its ability to connect ad exposure to actual customer outcomes. Rather than relying on clicks, views, or modelled assumptions, it links marketing activity to real-world transactions, providing a more complete picture of what happened after an ad was served.

What’s more, advertisers can measure clearly defined outcomes, including leads, sign–ups, bookings, or additional purchases. This means that rather than trying to ask which channel should receive credit for a sale, they can say with more certainty which channel drove it. It also supports broader business goals beyond just sales, helping brands and retailers acquire customers, generate leads, and nurture long-term relationships.

So, how do you measure post-transaction performance?

Closed-loop attribution, such as return on investment (ROI) and customer acquisition cost (CAC), can help provide a more complete view of media efficiency by connecting ad exposure directly to observed sales. However, incrementality testing is what allows advertisers to measure sales generated by advertising versus what would have happened without it through statistical holdout testing.

Incrementality testing isolates the causal effect of an ad by comparing the behavior of shoppers who’ve seen it against a control group that wasn’t exposed to the ad. It helps prove post-transaction placements’ effectiveness in driving net-new revenue rather than capturing consumers who would’ve converted regardless.

While it’s harder to measure than ROAS, it’s also more reliable. That being said, ROAS is, and will always be, a useful efficiency check.

The True Measure of Campaign Success

As investment in commerce media continues to grow, brands and retailers need greater confidence that their metrics reflect the current customer journey, as fragmented and disjointed as it is.

ROAS and other conventional attribution models will remain an important part of the measurement toolkit, but can’t answer every question.

The truth is, the industry has spent far too long measuring activity. Post-transaction measurement is what makes it possible to see impact instead — and incrementality testing is what proves it.

 See what post-transaction measurement looks like in practice instead.

Learn how Fluent In-Store helps brands and retailers transform checkout into a measurable media channel.