identifier_exists
identifier_exists is a yes/no attribute that tells the channel whether a product has a unique identifier like a GTIN or brand plus MPN, used to declare honestly when one genuinely does not exist.
Most branded retail products have a GTIN, and channels expect one. But some products legitimately have no universal identifier: handmade goods, custom items, vintage pieces, your own private-label products, or books published before ISBNs. For those, identifier_exists set to 'no' (or 'false') tells the channel not to expect one.
It matters because it prevents two opposite problems. Set incorrectly to 'no' on a product that actually has a GTIN, and you lose the matching and reach a real identifier would bring. Left implying an identifier exists when it does not, and the product can be disapproved for a missing GTIN.
In the feed, identifier_exists is usually only needed when the answer is 'no'; when you do supply valid identifiers, the channel infers they exist. The key is honesty: use 'no' only when the product truly has no standard identifier, not as a shortcut to skip filling in data you actually have.
MartechFlow can set identifier_exists automatically based on whether a product carries a valid gtin or brand-plus-mpn, so the flag always reflects reality and you are not manually toggling it across the catalog.