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How the Item ID Attribute Powers Performance in Google Merchant Center

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Ah, the humble id. On the surface, it looks like the most boring field in your Google Merchant Center feed—a throwaway value, right? Just toss a number in there and move on? Not so fast. The more I’ve worked with feeds across Shopify, custom CMS setups, and API-based platforms, the more I’ve realized just how foundational the id is to everything that follows in your Shopping and Performance Max campaigns. This unassuming attribute quietly determines whether Google remembers your product’s performance history, whether supplemental feeds map correctly, and whether dynamic remarketing works at all.

In this episode of Merchant Center Mastery, we’re unpacking the deceptively complex id attribute. We’ll dig into how it connects your data across systems, why changing it can wipe historical performance, and how to handle ids during feed transitions without breaking everything. Whether you're a brand scaling across multiple apps or just trying to get a single product listing approved, your id strategy might be more critical than you think.

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Video Transcript

(edited for reaedability)

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Why the id Attribute Matters More Than You Think

If you’ve been in the Merchant Center game long enough, you know some feed attributes feel like throwaways. id might seem like one of those at first glance. I get it. When I first sat down to plan this video, I wondered if it was even worth making. It’s just an identifier, right?

But the deeper I dug, the more I realized this little attribute touches almost everything in Merchant Center and Google Ads. From tracking performance history to dynamic remarketing feeds, id might actually be one of the most important things you get right—or wrong.

So let’s break it down.

The id Attribute: What It Really Does

The id is not your SKU. It’s not your MPN. It’s not your internal part number. It’s the value Google uses to recognize your product across its ecosystem.

And honestly, the exact value of the id doesn’t matter—so long as it’s unique within your feed. Google doesn’t care if your id is "1234" or "abc-widget-001." What it does care about is that you don’t change it randomly.

Why? Because Google ties performance history to that id. They literally say so in their documentation now: “If you change the id, you’ll overwrite your product and its history.”

We’ve seen this firsthand. Change the id, and you risk resetting your quality score, relevance signals, and bidding data. It’s like deleting the product and starting over. Sometimes that’s helpful, like when a product gets stuck in policy disapprovals. But more often, it’s not.

How Platforms Like Shopify Handle ids

If you’re using Shopify and an app like Simprosys to manage your feed, you’ve probably noticed that the id defaults to the Shopify variant ID. That’s fine—so long as it stays consistent.

What we’ve seen go wrong is when a client switches feed providers or apps, and the new system starts using a different id format. Suddenly, Google thinks all your products are new. Performance tanks. Visibility drops.

Rule of thumb: if you’re transitioning feeds, make 100 percent sure your id stays the same unless there’s a strategic reason to reset it.

Best Practices and Common Pitfalls

We usually recommend using your SKU as your id if you’re not already generating one from your eCommerce platform. It’s readable, traceable, and usually unique.

Avoid manually changing ids unless absolutely necessary. You want your feed to be dynamic and scalable, especially as new products get added. If your id is managed manually, you’re opening yourself up to errors and disconnects.

Here’s one weird but critical warning: id is case-sensitive. If your feed contains “ABC123” and your supplemental feed references “abc123,” Google sees two different products. This is especially tricky in supplemental feeds, where one small letter can break everything.

When to Reuse an id

Google says don’t reuse ids for new products. I say... it depends.

If your new product is truly a replacement—same category, same audience, mostly the same features—then yes, I’d consider reusing the id. You’re carrying forward performance data for something that’s effectively the same product.

But if the replacement is fundamentally different or you’re still selling the old version, assign a new id.

ids in Dynamic Remarketing and Feed Matching

Let’s talk about one more crucial use case for id: dynamic remarketing.

If you’re using PMax, Demand Gen, or Display remarketing, those flashy dynamic product ads you see across the web are powered by one thing—the id.

When someone visits a product page on your site, Google matches the id in your structured data with the id in your Merchant Center feed. That’s how the right product shows up later in an ad. No match, no retargeting.

So make sure your schema markup reflects the same id you’re using in your feed. If you’re on Shopify, good news—this is typically handled for you automatically. But it’s still worth double-checking.

Final Thoughts

You might think of id as just another technical field to fill in, but it’s so much more. It’s the backbone of how Google understands your products.

So here’s your takeaway:

• Set your id thoughtfully
• Keep it consistent
• Don’t change it unless you’re sure

And if you ever feel stuck, remember—Google is watching your id more closely than you might think.