How a Merchant Center product feed works
Shopping ads are not written by hand. Google builds each one from a structured list of your products, and that list is the feed. Every item is a row of attributes: an identifier, a title, a description, the page it links to, an image, a price, whether it is in stock, its brand, and a product identifier such as a GTIN where one exists.
You get that list into Merchant Center in one of a few ways. A file can be uploaded or fetched from a URL on a schedule; an ecommerce platform such as Shopify or WooCommerce can push it through an app or extension; larger catalogues use the API. Google then checks each row against its own requirements and against your live product page. If the price or availability on the page disagrees with the feed, the item is held back, because Google is protecting the shopper from arriving at a different price than the one advertised.
Two further pieces sit on top. Supplemental feeds add or override selected attributes without rebuilding the main file, and feed rules transform values on the way in — trimming a title, mapping your stock words to Google’s, filling a gap with a default.
Why the product feed matters
In Shopping and Performance Max there are no keywords to write, so the feed does the job keywords do in search: it decides which queries you are eligible for. A title that reads the way your customers search will surface for those searches; a title that is an internal product code will not. The feed is the campaign copy.
It is also the honesty layer of the account. Wrong prices and stale stock waste money on clicks that end in disappointment, and repeated mismatches risk items or the whole account being suspended. In markets where shoppers are cautious about paying online, arriving at a page that contradicts the ad damages trust well beyond the single sale.
Where product feeds go wrong
Stale data is the most common fault. A feed fetched once a day on a shop whose stock moves hourly will advertise items that have already sold. The second is thin titles and missing attributes, which quietly restrict how often items can appear at all. The third is ignoring the diagnostics tab until a large share of the catalogue is disapproved and nobody knows when it started.
How to act on it
Treat the feed as a product of its own with someone responsible for it. Check diagnostics on a schedule, fix errors before warnings, and confirm that price, availability and currency on the live page match what you sent. Write titles the way a customer would describe the item, leading with the words they would actually type rather than an internal code.
Where the shop platform cannot produce what Google wants, use supplemental feeds and feed rules rather than rebuilding the website. If the catalogue is large or changes constantly, structured product feed management pays for itself, because every disapproved item is a product that simply cannot be advertised. For the wider setup around it, see Google Merchant Center.