You're spending money on Google Ads. Clicks are coming in. But your ROAS shows zero, or the conversion numbers look suspiciously low. Sound familiar?
Broken conversion tracking is one of the most common and most expensive problems in Google Ads. When tracking doesn't work, you can't tell which campaigns are profitable, which keywords are driving revenue, and where your budget should go. You're flying blind.
The worst part? Most merchants don't know their tracking is broken until they've been wasting budget for weeks or months.
How conversion tracking breaks (the common culprits)
1. Duplicate conversion actions
This is the most frequent issue for Shopify merchants. Google Ads and Shopify both try to track conversions, and if you're not careful, you end up with two (or more) conversion actions firing on every purchase.
Here's how it happens: you set up Google Ads conversion tracking manually using a Global Site Tag. Then you install the Google Shopping app from Shopify, which creates its own conversion action. Now every purchase fires twice. Your ROAS looks incredible on paper, but it's a lie.
The fix: In your Google Ads account, go to Tools > Conversions. You should see all your conversion actions listed. If there are multiple "Purchase" or "Transaction" actions, check which one is set as "Primary" for bidding. Only one should be primary. Set the others to "Secondary" so they still collect data but don't inflate your bidding signals.
2. The Google Shopping app "Purchase" event
Shopify's Google Shopping app creates a conversion action automatically. This is fine if it's your only conversion action. But if you've also set up manual tracking, or if you're using Google Tag Manager, the two systems can conflict.
Check this by going to Google Ads > Tools > Conversions and looking at the "Source" column. If you see both a "Website" source and a "Google Analytics" or "Shopify" source tracking purchases, you likely have overlap.
3. Tag placement issues
The Google Ads conversion tag needs to fire on your order confirmation page and only on that page. If the tag is placed on every page (a surprisingly common mistake), every page view looks like a conversion. If it's missing from the confirmation page entirely, no conversions are recorded.
For Shopify stores, the conversion snippet typically goes in Settings > Checkout > Additional scripts. If this field is empty and you're not using the Google Shopping app or Google Tag Manager, your tracking isn't set up at all.
4. Cross-domain and redirect issues
If your checkout process redirects through a different domain (common with certain payment providers), the conversion tag may not fire because the session context is lost. Shopify's standard checkout generally handles this well, but custom checkout flows or third-party payment pages can break the chain.
5. Consent mode and cookie restrictions
With privacy regulations tightening globally, more browsers are blocking third-party cookies by default. Google's Consent Mode v2 affects how conversion data is collected when users don't consent to tracking. If your cookie consent banner is misconfigured or overly restrictive, you may be losing a significant portion of your conversion data.
How to diagnose your tracking in 10 minutes
Here's a quick diagnostic you can run right now:
Step 1: Check your conversion actions.
Go to Google Ads > Goals > Conversions > Summary. Look for:
- How many conversion actions exist?
- How many are marked "Primary"?
- What's the source of each one?
- Are any showing zero conversions over the last 30 days?
Step 2: Verify the tag is firing.
Install the Google Tag Assistant Chrome extension. Visit your store, add a product to cart, and complete a test purchase (you can refund it afterwards). Check if the conversion tag fires on the order confirmation page.
Step 3: Compare numbers.
Pull your Shopify orders for the last 30 days. Pull your Google Ads conversion count for the same period. If Google Ads shows significantly more or fewer conversions than Shopify orders attributed to paid search, something is off.
Step 4: Check attribution windows.
Google Ads defaults to a 30-day click-through attribution window. If your purchase cycle is longer, you may need to adjust. Conversely, if you have a very short purchase cycle (common for impulse buys), a 30-day window might over-attribute conversions to earlier clicks.
The real cost of broken tracking
When conversion tracking is broken, Google's Smart Bidding algorithms (tROAS, tCPA, Maximize Conversions) have bad data to work with. They'll optimise toward the wrong signals:
- If tracking overcounts, Smart Bidding thinks everything is working great and keeps spending aggressively on underperforming keywords.
- If tracking undercounts, Smart Bidding thinks nothing is converting and either bids too low (missing opportunities) or pauses what it considers unprofitable campaigns.
Either way, your budget allocation is wrong. You're paying more than you should for the results you're getting, or missing results you could be getting.
How oddly detects tracking issues
oddly's Conversion Tracking Audit continuously monitors the health of your conversion setup. It flags issues like:
- Multiple primary conversion actions (possible double-counting).
- Conversion actions showing zero data (possible broken tag).
- Significant discrepancy between Shopify orders and Google Ads conversions.
- Changes in conversion rates that suggest tracking degradation.
Instead of finding out weeks later that your tracking broke during a site update, oddly catches it within its monitoring cycle and alerts you immediately. The Watch tier shows you that issues exist; the Nudge tier gives you the full diagnosis and a fix guide.
Conversion tracking is not "set and forget"
The biggest mistake merchants make is treating conversion tracking as a one-time setup. In practice, tracking breaks all the time:
- Shopify theme updates can overwrite custom scripts.
- App installations can conflict with existing tags.
- Google's own product changes can alter how conversion data flows.
- Privacy regulations and browser updates change what data is collectible.
Regular auditing is essential. Whether you do it manually every month or use a tool like oddly to monitor continuously, the important thing is that someone is watching.