1. Nothing has sold yet
Ads amplify what a store already does. With no sales at all, paid traffic is the expensive way to discover whether the product works.
2. The margin cannot carry a click
If break-even ROAS is above 4x, the constraint is pricing or cost, not bidding. No agency fixes arithmetic.
3. Operations cannot take the volume
Doubling orders with a supplier who cannot ship them produces refunds and bad reviews, not growth.
4. You want a guaranteed number
Nobody honest can promise a ROAS before seeing the account. If that promise is what closes the deal for you, you will end up with whoever is most willing to say it.
An agency that will take any client at any spend in any vertical is describing a sales process, not a service.