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eCommerce: Cut PMax Cannibalization in 4 Weeks With Negative Keywords

Biplab Poddar
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Yes, you can add negative keywords to Performance Max, at both campaign and account level, but there’s a catch worth knowing before you touch a single setting: negatives only affect Search and Shopping inventory inside PMax. Display, YouTube, and Discovery placements carry on regardless. Add exclusions carelessly and you can starve PMax of the very queries that were converting, so treat this as a scalpel, not a blanket.

TL;DR:

  • Negative keywords in Performance Max only impact Search and Shopping inventory, requiring careful scope management to avoid starving valuable queries.
  • Campaign-level negatives are safer for specific exclusions, while account-level negatives carry higher risks and should be reserved for broader, sitewide issues.
  • Using exact or phrase match negatives is recommended initially, with broad match only after observing actual query triggers and results over a minimum four-week testing period.
  • Most advertisers operate with fewer than ten negatives; targeted, data-driven exclusions outperforms blanket restrictions in reducing waste without harming conversions.
  • Regular audits of search terms and performance metrics are essential to refine negatives, ensure continued relevance, and prevent unintentional elimination of profitable queries.
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Table of Contents

How do you add negative keywords to Performance Max?

Google Ads houses PMax negative keywords in a specific spot, and once you know the path, it takes seconds to find. Open your campaign, go to Keywords, then the Negative keywords tab. From there you choose whether the exclusion applies to that single campaign or to your entire account.

Campaign-level negatives are the default choice for most eCommerce advertisers. They let you block irrelevant queries for one product line without touching anything else you’re running. Account-level negatives sit above every campaign, including Search, Shopping and any other PMax campaigns you operate, so they demand more caution.

Here’s the sequence to follow inside Google Ads:

  1. Open the PMax campaign and click Keywords in the left-hand menu.
  2. Select the Negative keywords tab.
  3. Click the plus button and choose This campaign or Account depending on scope.
  4. Enter your terms, one per line, and pick a match type.
  5. Save, then check back within a week to confirm impressions dropped where expected.

Match type still matters inside PMax, the same as it does in Search. Broad match negatives block any query containing your term in any word order. Phrase match blocks the exact sequence of words, wrapped in extra text. Exact match blocks only that precise search, nothing broader. Most advertisers reach for phrase or exact match here because PMax negative keywords apply exclusively to Search and Shopping inventory, so a badly aimed broad negative can quietly cut off Shopping impressions you never meant to touch.

Limits have loosened considerably. Google originally capped PMax at 100 negative keywords per campaign during its beta rollout, a restriction that frustrated advertisers managing large catalogues. That ceiling has since risen to 10,000 negative keywords per campaign, which gives retailers with sprawling product ranges genuine room to work. Negative keyword lists, the shared lists you can apply across multiple Search campaigns, still aren’t supported inside PMax at the time of writing, so each campaign’s negatives are managed individually.

Pro Tip: Start every new PMax campaign with exact-match negatives only. Broaden to phrase match after a few weeks once you’ve seen which queries actually trigger impressions.

What impact will negatives have on your conversions?

Because negative keywords only touch Search and Shopping inventory, any drop in reported PMax conversions after adding exclusions could simply mean traffic shifted to Display or YouTube within the same campaign, or it could mean genuine volume loss. Telling the difference is the entire point of measuring properly.

Watch three signals together, not in isolation:

Run a controlled test rather than judging week to week. Hold your budgets, bids and creative steady, document baseline conversions and cost before you make any change, then give it a minimum of four weeks before drawing conclusions. That window matches what advertisers commonly use when testing brand exclusions against Search cannibalisation, and it’s long enough for PMax’s automated bidding to settle into a new pattern rather than react to short-term noise.

A useful benchmark: many PMax campaigns run with barely any negatives at all. Industry analysis has found large numbers of accounts operating with fewer than ten exclusions, or none whatsoever, which suggests most advertisers are leaving obvious waste on the table rather than over-restricting their reach.

Cross-check every exclusion against the Search terms report and PMax’s search category insights before and after the change. If a category you didn’t intend to block disappears, you’ve found your answer.

Should you use account-level negatives or brand exclusion lists?

Account-level exclusions belong in a narrower set of situations than most advertisers assume. Reserve them for genuinely sitewide problems, terms that have no business appearing anywhere in your account, such as job-seeker queries or blatant irrelevance to what you sell. Anything more targeted than that usually works better as a campaign-level negative.

Brand exclusion lists sit in a special category. If you’re deliberately steering branded searches away from PMax and back to a dedicated Search campaign, sequence matters enormously:

Sweeping account-level negatives carry real risk precisely because they touch every campaign at once. A term that seemed obviously irrelevant to one product line can quietly block a long-tail Shopping query that was converting for another. Advertisers testing brand exclusions typically build in a rollback plan before flipping the switch, not after spotting a problem.

Pro Tip: Never launch an account-level brand exclusion on a Friday afternoon. Give yourself a full working week to watch the data before a weekend where nobody’s monitoring the account.

What are good negative keyword examples for eCommerce?

Retail accounts tend to attract the same handful of irrelevant query patterns, no matter what they sell. Building your starter list around these themes saves weeks of trial and error.

Common exclusion themes worth adding from day one:

Match type changes what each of these actually does. A phrase match negative on “how to” blocks any query containing that exact phrase, which usually covers most tutorial-seekers. An exact match negative on “how to fix [product]” is narrower and safer if you’re worried about collateral damage to a legitimate query like “how to choose [product].”

Building the list itself follows a simple workflow:

  1. Pull the Search terms report for the trailing 30 to 90 days.
  2. Filter for terms with spend but zero conversions.
  3. Group similar terms into themes rather than excluding one query at a time.
  4. Add the highest-confidence exclusions first, phrase or exact match, and hold off on broad match until you’ve seen results.
  5. Review again in two weeks and expand the list based on what’s still leaking spend.

One workflow deserves special attention for advertisers running Search alongside PMax: when a query is a consistent top performer in Search, add it as an exact-match positive keyword in Search and simultaneously add an exact-match negative in PMax. This stops the two campaigns bidding against each other for the same auction, and it lets Search, which gives you more granular control, own the term outright. Tools that speed up this kind of search term analysis can shorten the discovery phase considerably.

How often should you audit your PMax negative keywords?

Negatives aren’t a set-and-forget setting. Run these reports on a fixed schedule rather than reacting only when something looks wrong:

Track total account conversions, blended CPA and ROAS, and branded impression share every time you make a change. These four numbers together tell you whether an exclusion helped or hurt, far more reliably than watching PMax’s own reported conversions in isolation.

Cadence matters as much as the metrics themselves. Check weekly for the first month after any negative keyword change, then drop to a monthly review once performance has settled.

Scripts and the Google Ads API can automate parts of this, flagging spend-without-conversion terms before you’d spot them manually. Reviewing your Shopping campaign structure alongside PMax negatives often reveals overlap you’d otherwise miss, and a red flags checklist is worth running after every significant change.

Pro Tip: Keep a simple spreadsheet log of every negative you add, the date, and the campaign’s conversion trend for the following two weeks. Six months in, that log becomes the best training material you’ll ever have for spotting which exclusions actually pay off.

How does Oxedent approach PMax negative keywords?

Oxedent treats exclusions as the last lever, not the first. The process starts with feed and asset quality, because a poorly matched product feed causes more wasted spend than most negative keyword lists ever will. Only once the feed and Shopping structure are sound does attention turn to search term data.

The instinct to exclude aggressively is understandable, but PMax’s bidding algorithm needs a reasonable pool of queries to learn from. Cut too deep, too fast, and you starve the very machine you’re trying to optimise. A four-week minimum test window, with baseline metrics locked in beforehand, is the difference between a considered exclusion and a guess.

That balance, between reducing wasted spend and preserving enough volume for the algorithm to keep learning, sits at the centre of every account Oxedent manages.

What the data actually tells us about negative keywords

The conventional advice on PMax negatives tends to swing between two extremes: either “don’t bother, the algorithm knows best” or “exclude everything remotely risky.” Neither holds up. The finding that a large share of PMax accounts run with fewer than ten negatives, or none, tells you most advertisers have swallowed the first extreme without testing it.

What the evidence actually supports is narrower and more useful: negatives work best as a targeted correction applied to specific, provable waste, not as a sweeping defensive measure. The four-week test window matters more than any single exclusion decision, because it’s the only thing standing between a real signal and a coincidence in the data. Advertisers who skip that step and judge results after four days are the ones who end up blaming negative keywords for problems the algorithm’s own learning curve caused.

Prioritise the Search terms report over instinct. Every exclusion should trace back to a query that actually spent money and didn’t convert, not a term that merely sounds irrelevant.

— Biplab

Get a free audit of your PMax negative keyword setup

Oxedent is the alternative to guessing your way through PMax settings alone. Where most advertisers either ignore negatives entirely or over-exclude out of caution, Oxedent applies the same conservative, data-led testing rhythm to every eCommerce account it manages, built on the discipline of proving waste before cutting it, not assuming it.

Oxedent’s PPC management service starts from £350 per month and covers Google Ads, Shopping and Performance Max campaigns for established online retail brands, with no long-term contract locking you in. If you’d rather see where your own account stands first, Oxedent offers a free Google and Facebook Ads audit that checks specifically for PMax cannibalisation risk, missed negative keyword opportunities, and whether your brand traffic is being protected or quietly leaking away. Book that audit and find out what your Search terms report has been trying to tell you.

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FAQ

Can you add negative keywords to PMax?

Yes. Google Ads lets you add negative keywords to Performance Max at both campaign and account level through the Keywords → Negative keywords tab. They only affect Search and Shopping inventory, so Display, YouTube and Discovery placements aren’t touched.

What is a negative keyword example?

A negative keyword blocks your ad from showing on a specific search, such as excluding “free” or “jobs” so your Shopping ads don’t appear for bargain-hunters or job-seekers searching your brand name. Match type determines how broadly that exclusion applies, from a single exact phrase to any query containing the word.

How do you make a negative keyword list?

Pull your Search terms report, filter for terms that spent money without converting, then group similar queries into themes like “free,” “cheap,” or job-related terms. Start with phrase or exact match on your highest-confidence exclusions and expand the list every two weeks as new patterns emerge.

What is a benefit of negative keywords?

Negative keywords cut wasted spend by stopping your budget going toward searches that were never going to convert, which improves blended CPA and ROAS across the account. In PMax specifically, they also help prevent auction overlap with your Search campaigns when a term is already a proven Search performer.

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