In classic paid media the feed is plumbing and the ad is creative. In GEA the feed is the creative. When an engine recommends a product it reaches for attributes: price, size, compatibility, materials, lead time, warranty, who it suits. Those attributes are what get quoted into the answer, so the quality of your feed is the quality of your creative.
The practical test is simple: take any constraint a buyer might state and ask whether a machine reading only your feed could verify it. "Waterproof" is a marketing word; "10,000mm hydrostatic head, taped seams" is a verifiable attribute. "Enterprise-ready" is a marketing word; "SOC 2 Type II, SSO via SAML, 99.9% SLA" can be checked.
Completeness matters more than cleverness. A feed missing price on 30% of items will lose every budget-constrained prompt for those items regardless of how good the rest of the record is. Coverage of the attributes your clusters actually reference should be tracked as a percentage and treated as a campaign health metric.
Disambiguation is the second discipline. Engines struggle with variants: the same product in three sizes, or a bundle that shares a name with its component. Clear parent-child relationships, unique identifiers and explicit variant attributes stop the engine from hedging or picking the wrong item.
Freshness is the third. An engine that has learned a stale price will keep repeating it, and a correction takes time to propagate. Feeds that update on a predictable schedule, with change history the engine can see, earn more trust than feeds that jump erratically.
Treat the feed like a creative asset with an owner, a review cycle and a change log. The agencies that win GEA reviews are usually the ones who brought a feed coverage report to the meeting, not the ones who brought new headlines.