A brand sells a perfume through department stores and also wants to list it online. On a large marketplace, the same bottle might be offered by the brand, by an authorised distributor and by several resellers. How does the marketplace know they are all selling the same thing, and how does it stop sellers inventing product numbers? Product identity is at the centre of both questions.
The marketplace catalogue problem
A marketplace hosts one catalogue shared by many sellers. Shoppers expect one product page for one product, with competing offers listed on it, not dozens of near-identical pages. To achieve that, the marketplace needs a reliable way to say "these listings are the same item".
The GTIN (Global Trade Item Number) is the obvious key. It is assigned by the brand from its GS1 Company Prefix, it is globally unique, and it is already printed on the pack. For the basics of how that number works, see what is a GTIN?
How marketplaces check GTINs
Because sellers type GTINs into listing forms, a marketplace has to guard against wrong or made-up numbers. Amazon is explicit about one check it makes. Its seller guide on GTIN exemptions says:
"We verify the authenticity of product UPCs by checking the GS1 database. UPCs that do not match the information provided by GS1 will be considered invalid."
(UPC is the 12-digit form of GTIN common in North America.) The same guide recommends getting UPCs directly from GS1.
Amazon does not spell out every detail of the check, but GS1's registries, queried through services such as Verified by GS1, record which company a GTIN is licensed to and hold a small set of core product attributes. This is one reason brands are advised against buying cheap numbers from third-party resellers: a number licensed to someone else may not match the brand selling it. How licensing works is covered in what does a GS1 Company Prefix actually do?
A matching GTIN tells the marketplace the number is properly issued and licensed to the brand. It does not prove that a particular item a seller ships is genuine. That is a separate problem, addressed by other controls.
The marketplace's own identifiers
Alongside the GTIN, marketplaces assign their own internal identifiers to catalogue entries. On Amazon this is the ASIN (Amazon Standard Identification Number). Other marketplaces use their own equivalents.
It helps to keep the two apart:
| GTIN | Marketplace ID (e.g. ASIN) | |
|---|---|---|
| Assigned by | The brand, from its GS1 licence | The marketplace |
| Identifies | The product, wherever it is sold | A catalogue entry on that marketplace |
| Used by | Retailers, distributors, marketplaces, warehouses | That marketplace and its sellers |
| Travels with the product? | Yes, printed on the pack | No |
The GTIN is the brand's portable product identity. The marketplace ID is the marketplace's handle for its own page.
Exemptions for products without a GTIN
Some products legitimately lack a GTIN: handmade goods, some private-label items, certain parts. Amazon runs a GTIN exemption process for such cases. Its guide describes applying for an exemption and supplying product images that show the brand on the product or its packaging.
Beyond that guide, the details — which categories require a GTIN, which accept an exemption, and what evidence is needed — are set on the marketplace's seller pages, can differ by region and category, and change over time. We have not reproduced them here. Always check the marketplace's current rules for your category before you list.
Who controls the product page?
When several sellers offer the same GTIN, the product page's title, images and description are assembled from what sellers contribute. Brand owners often want more say over that content. Major marketplaces offer brand programmes (Amazon's is called Brand Registry) that let a verified brand owner manage how its branded products appear and report problems such as listings that misuse the brand.
Eligibility, verification steps and benefits vary by marketplace and change over time, so treat any summary, including this one, as a starting point. Consistent master data helps here too: if the data you send to retailers and marketplaces agrees, it is easier to correct a page that has drifted. The data flow behind that is described in how product information gets from a brand to a retailer.
Online and in-store: one identity
Online orders don't pass through a checkout scanner, but the GTIN still does the same job as at a till: it ties a sale to a known product. In a physical store, the till looks the GTIN up in the retailer's item file, as described in what happens when a product is scanned at the checkout. On a marketplace, the GTIN links the listing to the catalogue entry. Using one GTIN per product across every channel keeps those records aligned.
A worked example
Maison Ardent, a fictional perfume house, sells Ambre Nuit 100 ml through stores and plans a marketplace listing.
- The bottle already carries a GTIN from Maison Ardent's GS1 licence, used by every retailer.
- Maison Ardent lists the perfume using that GTIN. The marketplace checks it against GS1's data and finds it licensed to Maison Ardent.
- The marketplace creates a catalogue entry with its own internal ID. Two authorised distributors later add offers to the same entry, using the same GTIN.
- Maison Ardent enrols in the marketplace's brand programme, where offered, to help manage the page's images and description.
- A year later, Maison Ardent launches a 50 ml bottle. A different net content makes it a different trade item, so it gets its own GTIN and its own catalogue entry.
Practical advice
- License your own GTINs from your local GS1 office and register core attributes, so marketplace checks succeed.
- Use one GTIN per product across all channels.
- Keep master data consistent across retailers and marketplaces.
- Check current marketplace rules for your category and region before every new listing.
- Remember that the marketplace owns the customer relationship for sales it handles. Ways brands can build their own relationship after the sale are discussed in why connected packaging can create a direct brand relationship.