Last-click is the wrong way to measure top-of-funnel because it will always undervalue the channels that introduce people to your brand. Taylor Holiday made the essential point on Ecommerce Playbook that when you obligate yourself to measure only the very last click, you force your ad dollars toward the end of the customer journey. You end up fighting over customers who are already about to buy, which isn’t the goal of top-of-funnel spend.
Philippe Roireau echoed this on Ecommerce Coffee Break, explaining that last-click attribution naturally favors bottom-funnel channels, like Google search, that are meant for converting existing demand. Instead, he suggests using models that put more weight on the first touches from channels like Facebook or TikTok that drive discovery. While multi-touch models can get complicated, the most practical solution that kept coming up is the simple post-purchase survey. On Honest Ecommerce, Matt Bahr argues that productizing the question "How did you hear about us?" is the most direct way to get your top-of-funnel attribution right.
Your most effective first step is to implement a simple post-purchase survey. As Feifan Wang said on Ecommerce Coffee Break, comparing this zero-party survey data against your last-click analytics is like going into high-def. You see what the platform claims credit for, and you also see what the customer actually remembers as their starting point. This blended view gives you a much more honest picture of what’s really working.