When ROAS drifts upward or slumps without warning, it can feel like a quiet signal from the marketplace asking to be decoded. Behind every shift lives a cluster of possible forces: budget decisions, auction dynamics, customer intent, creative relevance, and even the subtle tide of seasonality.
This article walks through the most common reasons performance may rise or fall, the diagnostic checks that help pinpoint what’s really moving the numbers, and the practical actions teams can take to restore balance. Think of it as a companion field guide to the ROAS Inspector for navigating ROAS changes with clarity, confidence, and a sharper sense of what’s actually driving the story.
Higher Cost Per Click (CPC)
What happened: We paid more for the same search terms.
Why it may have happened:
Increased competition in the auction (more advertisers bidding on the same terms).
More aggressive bidding or tightening of targets.
Algorithmic shifts in Amazon’s auction dynamics.
What to check / what could be done:
If competition caused the increase, there may be limited control—consider testing new keywords to widen coverage.
If bids rose due to your own strategy, confirm it was intentional.
Review placement multipliers and rule-based optimizations that may be pushing CPCs up automatically.
Look for shifts in budget allocation that may have forced bids higher.
Lower Conversion Rate (CR)
What happened: For the same search terms, customers purchased less often.
Why it may have happened:
Changes in product detail page quality (content updates, imagery, pricing, or availability).
Shifts in reviews: lower average rating, new negative reviews, or fewer recent reviews.
Competitor improvements (pricing, content, availability, badges like Best Seller).
Changes to ad placements or audiences (e.g., showing up more in top-of-search vs. product pages).
Different product being shown in ads (for campaigns with multiple ASINs).
Seasonality or changes in shopper intent.
What to check / what could be done:
Compare against organic CR to isolate whether it’s an ads issue or a product issue.
Confirm the advertised ASINs did not change.
Check for placement distribution shifts or new creative/targeting setups.
Review competitors’ pages for improvements or promotions.
Lower Average Order Value (AOV)
What happened: Customers spent less per purchase for the same search terms.
Why it may have happened:
Product price reductions or applied discounts.
Changes in pack size or quantity for bulk items.
Seasonality (shoppers buying smaller or cheaper items).
Different product being served in ads (e.g., promoting a cheaper SKU unintentionally).
Shift in product mix within campaigns.
What to check / what could be done:
Verify whether the product shown in ads changed.
Review pricing changes or promotions that dropped off.
Check whether spend shifted toward lower-priced ASINs.
Confirm whether the change was intentional (e.g., focusing on entry-level products).
Mix Shift (Ad Spend Mix)
What happened: More ad spend moved toward higher- or lower-ROAS search terms.
Why it may have happened:
Bid or budget changes that favor certain terms.
Auction competition causing Amazon to redirect spend.
Strategic shifts (e.g., intentionally moving from branded to non-branded).
Auto/broad campaigns exploring new terms.
What to check / what what could be done:
Confirm whether the shift was intentional; if not, adjust targets or bid rules.
If lower-performing terms started receiving more spend, consider tightening ACOS/goals.
For auto or broad campaigns, increase harvesting or add negatives for better control.
Review campaign structure to ensure the right terms have the right budgets.
Higher Spend in Non-Performing Ads
What happened: We spent more money on search terms that don’t convert.
Why it may have happened:
More spend going toward broad or auto campaigns.
Exploration of low-data or speculative keywords.
An increase in irrelevant queries slipping through due to incomplete negative keyword lists.
Seasonal shifts causing normally reliable terms to underperform.
What to check / what could be done:
If low-data targets are receiving too much spend, review initial CR/AOV assumptions or tighten bids.
Add negatives for irrelevant or poor-performing terms in auto/broad campaigns.
Review max ACOS targets—if too aggressive, spend will flow to weaker terms.
Consider segmenting exploratory campaigns so they don’t overshadow proven performers.
Additional Optional Causes To Consider
Inventory / Availability Issues – Running low on stock or going in/out of stock can affect CR and mix.
Coupon / Promotion Changes – Ending a promo can hit CR; starting one can reduce AOV temporarily.
Detail Page Latency or Outages – Occasional Amazon site performance issues can subtly reduce CR.
Delivery Promise Changes – Longer delivery windows can drop CR, especially on non-Prime ASINs.