Google Analytics 4 is a powerful general-purpose analytics tool. But "general-purpose" is the key phrase. When it comes to e-commerce-specific needs — particularly attribution and profit tracking — GA4 has significant blind spots that most merchants aren't aware of.
Data Sampling
GA4 samples your data when you run reports that exceed its processing thresholds. For stores with significant traffic, this means the numbers you're looking at aren't exact — they're estimates. You might be making budget decisions based on data that's 80% accurate rather than 100%.
This is particularly problematic for smaller segments. Looking at a specific campaign's performance in a specific region? The sample size might be too small for the estimate to be meaningful.
Attribution Black Box
GA4's data-driven attribution model uses machine learning to assign credit across touchpoints. Sounds great in theory. In practice, you can't see the model's weights, you can't understand why it credits one channel more than another, and you can't compare it against other models to validate its conclusions.
When you can't understand the model, you can't trust it for high-stakes budget decisions. You're essentially outsourcing your marketing strategy to an opaque algorithm.
No Native Profit Tracking
GA4 tracks revenue. It does not track profit. It doesn't know your COGS, your shipping costs, your return rates, or your ad spend per channel. You can set up custom events and import cost data, but it's manual, fragile, and incomplete.
A channel showing £50K in revenue looks great until you realise it cost £45K in ads to generate. GA4 won't tell you that without significant custom configuration that most merchants don't implement.
Cross-Domain and Cross-Device Gaps
If your checkout is on a subdomain, or you use a third-party checkout like Shopify's, GA4's cross-domain tracking is notoriously finicky. Sessions break, attribution is lost, and your conversion data becomes unreliable.
Cross-device tracking requires users to be logged in with Google accounts — which gives you a partial picture at best.
The 24-48 Hour Data Delay
GA4's data processing isn't real-time. For some reports, you're looking at data that's 24-48 hours old. If you're running a time-sensitive campaign and need to make adjustments based on performance, this lag can cost you real money.
When GA4 Is Enough (and When It Isn't)
GA4 is perfectly adequate if you need general website analytics — page views, user flows, basic event tracking. It's free and it's good at what it does.
But if you need accurate multi-touch attribution, profit-per-channel visibility, real-time data, and e-commerce-specific insights like revenue leak detection — you need a purpose-built tool alongside GA4, not instead of it.