Questions · Evaluate
What identifier do I use if my products have no barcodes?
Publish a manufacturer part number of your own and keep it stable. The value of an identifier is not that it is registered with anybody, it is that the same product carries the same string wherever it appears: your product page, your feed, a marketplace listing, a comparison site. That property is what lets an agent decide two listings are one product, and it does not require a GTIN. Inventing one and then changing it is worse than having none.
Why it happens
Identifiers are how a product becomes the same product across sites. A shopper who names a model, or who saw the item elsewhere, gives the agent a string it must resolve to something in your catalogue. With an identifier that resolution is exact. Without one it is fuzzy text matching against your merchandising titles.
This is quietly decisive in comparison, because a store that can be matched exactly is a store that can be included in a price comparison at all.
This comes up at the Evaluate stage. The full treatment, including how to reproduce it and what to change, is on Products have no GTIN or MPN to match against.
Related questions
Run a free scan and find out which of these your store actually hits.