The ceiling arrives fast
Search demand for a single product is finite. Once you own most of the available impressions, more budget buys worse traffic rather than more sales.
What breaks it
- Adjacent search intent — problems and use cases rather than the product name.
- Demand creation via Demand Gen or YouTube, to grow the pool of people who know the category.
- New markets, if operations can serve them.
- AOV work — bundles and upsells raise what each of the same customers is worth.
The trap
Raising budget into a saturated auction and blaming the agency when efficiency falls. The constraint is demand, not management.