The Averaging Problem
Multi-category retailers face a fundamental tension: Google Ads optimises toward a single target, but your products have wildly different economics.
When you set a 4x ROAS target across your entire catalogue, you're telling the algorithm that every sale is equally valuable. It isn't. A £50 sale at 65% margin is worth £32.50 in gross profit. A £50 sale at 10% margin is worth £5.
The algorithm doesn't see margin. It sees revenue. And it will happily spend £12 to get that £50 low-margin sale, destroying your contribution margin in the process.
Multi-category retailers with 1,000+ SKUs across 10+ categories routinely see 40-60 percentage point margin variance. A single ROAS target cannot account for this spread.
How It Happens
The trap springs gradually. Here's the typical progression:
1. Initial Setup
Agency or in-house team creates one Shopping campaign with a target ROAS based on blended margin. "We average 35% margin, so 3x ROAS should work."
2. Algorithm Learns
Smart Bidding discovers which products convert easily. Often, these are lower-margin commodities with high search volume and clear purchase intent.
3. Spend Shifts
Budget gravitates toward easy conversions. Low-margin categories consume more spend. High-margin products get starved of visibility.
4. The Trap Closes
ROAS looks fine. Revenue grows. But contribution margin shrinks because you're scaling low-margin categories while high-margin products sit idle.
Real-World Example
A general merchandise retailer with 8,000 SKUs across home, electronics, and accessories ran a single Shopping campaign at 3.5x ROAS target. Here's what the category breakdown revealed:
Category Performance Analysis
70% of spend went to categories generating less than 0.5x POAS. The high-margin categories that could have delivered 2.5x+ POAS were starved of budget because they had lower conversion volume.
The Result
Blended ROAS showed 3.8x. Actual contribution margin after accounting for category mix: negative £12,000/month. The "successful" campaign was losing money.
The Damage Done
Category averaging doesn't just waste money. It creates compounding problems:
Algorithm Mis-Training
Smart Bidding learns that low-margin products are "good" because they hit ROAS targets easily. This bias becomes harder to reverse over time.
Opportunity Cost
Every pound spent on a 12% margin product could have been spent on a 60% margin product. The gap compounds monthly.
Inventory Distortion
Ads drive demand toward low-margin products, creating reorder pressure on items you'd rather sell less of.
Reporting Blindness
Blended metrics look healthy, masking the category-level destruction. Problems only surface when finance investigates.
Detecting the Trap
Three diagnostic questions reveal whether you're trapped:
1. What's Your Margin Variance?
If your highest-margin category is 40+ percentage points above your lowest, a single ROAS target is definitionally wrong for one of them.
2. Where Does Spend Concentrate?
Pull category-level spend reports. If 50%+ of spend goes to your lowest-margin categories, the algorithm is optimising for volume, not profit.
3. What's Category-Level POAS?
Calculate profit on ad spend for each category separately. If any category shows sub-1x POAS, you're subsidising loss-making spend with high-margin wins.
The Solution
Escaping the category averaging trap requires structural change:
1. Segment by Margin Tier
Group products into 3-4 margin tiers. Create separate campaigns or asset groups for each tier with margin-appropriate ROAS/POAS targets.
2. Use Custom Labels
Implement custom labels in your product feed to flag margin tiers. Use these for campaign segmentation and reporting.
3. Set Tier-Specific Targets
High-margin products can tolerate lower ROAS targets (more aggressive bidding). Low-margin products need higher ROAS targets to remain profitable.
4. Consider Exclusions
Some products shouldn't be advertised at all. If a 10% margin product needs 8x ROAS to break even, and you can't achieve that, exclude it.
The goal isn't to advertise everything. It's to advertise profitably. Sometimes that means not advertising at all.
Frequently Asked Questions
What is the category averaging trap in Google Ads?
The category averaging trap occurs when you apply a single ROAS target across product categories with vastly different margins. A 4x ROAS target that works for 60% margin products destroys profitability when applied to 15% margin products. The average looks acceptable while individual categories bleed cash.
How do I know if I'm falling into the category averaging trap?
Check if you're running one campaign with a single ROAS target across multiple product categories. Then compare the margin profile of each category. If margin variance exceeds 20 percentage points across categories, a single target is almost certainly destroying value somewhere.
Should I run separate campaigns for each product category?
Category-specific campaigns or asset groups with margin-appropriate targets are essential for multi-category retailers. The structure depends on catalogue size, but the principle is constant: products with different margins need different targets. A phone case at 70% margin and a cable at 12% margin cannot share a ROAS goal.
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