Diagnostic Insight
Seven Google Ads Decisions to Question
These seven questions help you examine where reporting and commercial outcomes can diverge. They are not ranked findings from an audit dataset.
What are the most expensive Google Ads mistakes for ecommerce?
The costliest errors in ecommerce Google Ads are bidding on revenue instead of profit, treating every SKU the same, ignoring post-sale costs like returns and fees, scaling past the profit cliff, neglecting negative keyword governance, running Performance Max without guardrails, and working with misaligned agency incentives.
Bidding on Revenue, Not Profit
Target ROAS treats every pound of revenue equally. A £100 sale at 60% margin and a £100 sale at 12% margin get the same bid priority. The algorithm chases volume, not value - and your P&L absorbs the difference.
Commercial Cost
Spend on low-contribution products can leave too little to cover advertising
What to Check
A high-ROAS campaign may still favour low-contribution products. Compare the product mix with the finance view.
Treating Every SKU the Same
Most accounts group products by category. But a hero SKU generating 40% of contribution margin shouldn't share budget with a clearance line at 8% margin. Without SKU-level roles, your best products subsidise your worst.
Commercial Cost
Budget can go to products that cannot support their acquisition cost
What to Check
Ask which products receive spend and what each contributes after product and fulfilment costs.
Ignoring Post-Sale Economics
Returns, BNPL fees, platform charges, and fulfilment costs aren't reflected in Google Ads data. A campaign reporting 5x ROAS might deliver 1.2x after real costs - or worse, a loss. Yet most accounts optimise as if the sale is the finish line.
Commercial Cost
Returns and fees can change contribution after the attributed sale
What to Check
Returns can turn an attractive revenue report into a weaker contribution result. Compare recognised sales with net orders.
Scaling Past the Profit Cliff
Every account has a point where incremental spend destroys incremental profit. Marginal CPAs rise, conversion rates fall, and each additional pound generates diminishing returns. Most accounts blow past this point because they're watching top-line ROAS.
Commercial Cost
Extra spend may not leave enough incremental contribution to pay for itself
What to Check
Compare the contribution from additional spend with its cost rather than assuming the next budget increase will perform like the average.
No Negative Keyword Governance
Search term reports are getting less transparent, but that's not an excuse to stop managing them. Without systematic negative keyword management, you're paying for irrelevant, competitor, and informational queries that will never convert profitably.
Commercial Cost
Irrelevant searches can consume budget without supporting the business
What to Check
Accounts where broad match has been enabled without corresponding negative keyword infrastructure. The algorithm is efficient at spending budget - it's not efficient at knowing which clicks your business can actually profit from.
Performance Max Without Guardrails
PMax consolidates campaigns into a black box and allocates budget across channels automatically. Without asset group segmentation, audience exclusions, and feed quality controls, you've handed Google a blank cheque with no commercial constraints.
Commercial Cost
Uncontrolled brand cannibalisation and margin-blind allocation
What to Check
PMax campaigns reporting strong ROAS that are predominantly serving brand queries - traffic you'd have captured organically. Strip out brand, and the incremental performance often collapses.
Misaligned Agency Incentives
If your agency charges a percentage of ad spend, their revenue grows when your spend grows - regardless of whether that spend is profitable. This creates a structural incentive to scale first and ask questions later.
Commercial Cost
Systematic over-spending driven by commercial misalignment
What to Check
Agencies recommending budget increases with projected ROAS improvements - but no mention of margin, contribution, or whether the additional spend will actually generate profit after real costs.
The Common Thread
Every one of these mistakes shares the same root cause: the account is optimised for a metric that doesn't align with commercial reality.
Google Ads is a media buying platform. It's excellent at what it does - acquiring clicks efficiently against a target. But it has no concept of your margins, your return rates, your fulfilment costs, or your cash flow cycle.
These seven mistakes persist because fixing them requires commercial fluency - not just platform expertise. The fix isn't better Google Ads management. It's better commercial thinking applied to Google Ads management.
How Many Apply to Your Account?
Our eCommerce Google Ads audit diagnoses exactly which of these mistakes are present in your account - and quantifies the commercial impact of each.
Frequently Asked Questions
How do I know if my Google Ads account has these problems?
The clearest signal is a disconnect between what your agency reports and what your finance team sees. If reported ROAS looks strong but contribution margin is flat or declining, at least one of these mistakes is likely present. Our eCommerce Google Ads audit is designed to diagnose exactly which ones apply to your account.
What's the most common expensive mistake you find?
Bidding on revenue instead of profit. It's the foundation that every other mistake builds on. When the algorithm optimises for the wrong metric, every downstream decision - budget allocation, SKU prioritisation, scaling thresholds - compounds the error.
Can these be fixed without changing agency?
Some can. Negative keyword governance and PMax guardrails are operational fixes any competent agency can implement. But profit-based bidding and SKU-level economics require infrastructure and commercial fluency that most generalist agencies aren't set up for.
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