Google Ads for Ecommerce: Why PMax Isn't Your Whole Strategy

Why Most Ecommerce Brands Are Wasting Their Google Ads Budget

You're spending real money on Google Ads. PMax is running, Shopping campaigns are live, maybe there's a search campaign ticking in the background. But the numbers don't quite add up. Your blended ROAS looks decent, but when you strip it out by channel, Google is eating into contribution margin in ways Meta never did.

This is the most common situation we see when we audit a Google Ads account for an ecommerce brand. Not catastrophic. Not obviously broken. Just quietly inefficient, in ways that compound over months.

If you're spending $10K,$200K/month on Google and you haven't recently done a proper structural review, this post is for you. We'll break down how to think about Google Ads for ecommerce, why PMax alone isn't a full strategy, and what the top-performing accounts are actually doing differently.

The Problem With "Just Run PMax"

Performance Max launched to genuine fanfare. One campaign type, all placements, Google's machine learning doing the heavy lifting. It sounded like the answer to ecommerce complexity.

The problem isn't that PMax doesn't work. It does, for certain account types, at certain stages. The problem is that agencies and in-house teams started treating PMax as a replacement for a Google strategy, rather than one component of one.

Here's what happens when PMax runs without supporting campaigns:

Google will default to your highest-intent, easiest-to-convert traffic first. Brand searches. Retargeting audiences. Shoppers who were already 80% of the way to buying. The ROAS looks great because you're capturing demand that would have converted anyway. Meanwhile, net new customer acquisition is barely happening.

A skincare brand we work with came to us with a 2.8x ROAS on Google. Looked healthy. But when we dug into the new vs returning customer split, over 70% of Google purchases were from existing customers. Net new customer ROAS? 0.9x. The account was essentially spending ad budget to resell to people who already knew and liked the brand, and doing almost nothing for growth.

PMax is a brilliant tool for closing the funnel. It's a poor tool for opening it.

The Three-Layer Google Ads Structure That Works

The ecommerce brands consistently outperforming on Google aren't running one campaign type. They're running a deliberate three-layer structure that separates intent stages.

Layer 1, Brand and Retargeting (high-intent, high-ROAS)

This layer captures people who are actively looking for you or have already visited your store. Brand search campaigns, Shopping campaigns with brand exclusions removed, remarketing lists. The CPCs are lower, the conversion rates are higher, and the ROAS is strong.

This layer should be tightly controlled. You want maximum impression share on branded terms. Any competitor bidding on your brand name? That's a problem to solve here.

Layer 2, Category Shopping (mid-intent, volume)

Standard Shopping campaigns, not PMax, targeting your core product categories. This is where the bulk of new customer acquisition happens. The keyword signals are broader, the CPC is higher, and the ROAS will be lower than your brand campaigns.

This is where most brands underinvest because the ROAS looks worse than PMax. But the question isn't "what is the ROAS?" It's "what is the net new customer CAC, and is it within target?"

A food and lifestyle brand we manage grew gross sales by 77% month-on-month. A big part of that was identifying that their Shopping campaigns were profitable on new customers at a CAC the business could sustain, and scaling budget into that layer while keeping PMax tightly controlled on warm audiences.

Layer 3, PMax (full-funnel support)

PMax running in this context is a different beast to PMax running alone. It's not trying to do everything; it's plugging the gaps, YouTube, Display, Discover placements where there's incremental reach. Feed it strong creative assets. Set audience signals that reflect your actual customer profile. And exclude brand terms so it isn't cannibalising Layer 1.

The key metric to watch here isn't ROAS. It's whether PMax is adding reach that the other campaigns can't capture.

What Your Feed Quality Is Doing to Your Results

Most ecommerce brands treat their Merchant Centre feed as a one-time setup job. Upload the products, tick the box, move on. This is one of the most expensive mistakes in Google Ads.

Google's Shopping algorithm uses your product feed the same way Meta uses your ad creative. It's the raw material. Bad feed quality means the algorithm is working with incomplete information, which means your ads appear for irrelevant queries, your CTR drops, your Quality Score declines, and your CPC climbs.

The things that matter most in a well-structured feed:

Product titles. Google matches queries against your title first. Most default Shopify export titles look like this: "Blue Suede Shoe, SKU001." The optimised version: "Women's Blue Suede Ankle Boot, Cushioned Sole, Size 6,12." Keyword intent, product attributes, variant information. All in the title.

Product type vs Google category. Google's taxonomy has thousands of categories. Most brands map roughly. The brands outperforming on Shopping map precisely, it affects which auctions you're eligible for.

Custom labels. These let you segment your Shopping campaigns by margin, seasonality, bestseller status, or clearance. Without custom labels, you're bidding the same on a 60% margin product as a 15% margin product. That's contribution margin leaving the building quietly, every day.

The Attribution Problem Nobody Talks About

Here's an uncomfortable truth about Google Ads for ecommerce: last-click attribution makes Google look better than it is. Google reports the sale when someone clicks a Google ad and converts. But that person may have seen a Meta ad three days earlier that actually drove the consideration. Google just happened to close.

This is why blended MER (Marketing Efficiency Ratio, total revenue divided by total ad spend) is a more honest lens than channel ROAS. It tells you whether the whole machine is generating more revenue than it costs, without getting distracted by which platform gets "credit" for which conversion.

The brands we've seen scale Google Ads most effectively do two things: they monitor blended MER weekly, not just channel ROAS, and they have a separate new-customer acquisition metric to track whether Google is actually building the business or just servicing existing demand.

A jewellery brand in our portfolio runs weekly blended MER reporting across Meta, Google, and email. Their Google Shopping campaigns run at a 2.2x reported ROAS, below what most agencies would call "good." But their blended MER is 3.8x, their new customer CAC on Google is within target, and their email list is growing because Google is consistently bringing in first-time buyers who then convert through flows.

That 2.2x is a feature, not a bug. It's buying new customers efficiently. Without that framing, a nervous brand or an inexperienced team would have cut the budget months ago.

When to Use Google Search for Ecommerce

Shopping tends to dominate the conversation in ecommerce Google Ads, and for good reason, the intent match is strong, the visual format drives clicks, and the CPC is often lower than search.

But there are scenarios where Search campaigns add genuine incremental value:

High-consideration products. The more research a buyer does before purchasing, the more valuable it is to be present during that research phase. Supplements, tech accessories, furniture, skincare with clinical claims, buyers are searching "best NMN supplement for energy" or "do collagen powders actually work" before they buy. A Search campaign targeting those educational queries puts you in front of buyers at the moment of consideration, not just at the moment of transaction.

Competitor conquest. If a competitor is running aggressive Shopping campaigns in your category, Search lets you target their branded terms. Not cheap, and it requires careful copywriting, but in competitive categories it can carve out meaningful share.

Branded protection. Essential if you're spending on any upper-funnel activity. When Meta or TikTok drives awareness and someone later Googles your brand name, you need to own that result. Without a brand search campaign, you're handing that high-intent traffic to whoever is willing to pay for it.

How to Audit Your Google Account in 30 Minutes

If you haven't done a structural review recently, here's a quick-start process.

First, pull a search terms report for the last 90 days. Filter for terms with more than 5 clicks and below a 2x ROAS. This is the waste report. Add negatives aggressively. Most accounts have hundreds of irrelevant search terms burning budget, especially in PMax.

Second, check your new vs returning customer split in Google Analytics. If more than 50% of your Google conversions are from returning customers, your campaigns are over-indexed on retargeting and brand. You're buying loyalty, not growth.

Third, review your asset group scores in PMax. Any "Poor" or "Good" asset groups need attention. Feed PMax your highest-quality creative, lifestyle imagery, strong headlines that address a specific problem, and video if you have it.

Fourth, check your budget allocation across campaign types. If more than 60% of your total Google budget is sitting in PMax, redistribute. You're leaving Shopping intent uncaptured and brand protection underfunded.

Fifth, run a product-level performance report. Sort by spend. Identify your top 20% of products by spend and check their conversion rates. Are you spending on products that don't convert? Pull budget from poor converters, allocate to known winners.

What "Good" Looks Like on Google

These aren't universal benchmarks, every category, margin structure, and product price point shifts what's acceptable. But here are the ranges we target across client accounts:

• Branded Search: 8x+ ROAS (you should dominate your own brand terms)

• Category Shopping: 2.5,4x ROAS (depends heavily on AOV and margin)

• PMax (supporting role): 3,4x ROAS (with audience signals, excluding brand)

• Blended Google MER: 2x+ (factoring in brand + shopping + PMax together)

If your Shopping campaigns are below 2x and you haven't done a feed audit in the last 3 months, start there before touching bids.

The Bigger Picture: Google and Meta Working Together

The most common mistake we see in ecommerce media buying isn't a Google problem or a Meta problem in isolation. It's treating the two platforms as separate budget decisions instead of a connected system.

Meta drives discovery. Google captures intent. If Meta is spending efficiently on new audiences, you'll see an increase in branded Google searches within 2,4 weeks. That's the feedback loop that healthy ecommerce growth looks like. If your Google branded volume isn't growing while Meta spend is up, something is broken in your creative or targeting.

If you want to see how this structure applies to your specific account and what a proper Google Ads audit looks like in practice, that's exactly what we cover in our Growth Diagnostic Call. Thirty minutes, your actual account data, no generic recommendations.

Book a Growth Diagnostic Call here and we'll show you specifically where the inefficiency is and what to do about it.

If you're interested in how we approach the Meta side of this equation, our Growth Engine breaks down the full paid acquisition system we run across both platforms.