How to run the math yourself
On Google Ads, compare account performance before and after the agency arrived, with one adjustment: separate brand from non-brand, so existing demand for your name does not flatter the numbers. The agency's contribution lives in non-brand efficiency, recovered wasted spend, and growth the account could not produce before.
On SEO, track organic revenue, not just traffic. Visits to informational pages are an input; purchases and leads from organic search are the output. An agency that reports rankings without revenue is showing you the scoreboard from a different game. Run the comparison quarterly rather than monthly, because single months swing on seasonality and noise that have nothing to do with the agency.
Signals the fee is buying real work
Worth shows up in observable behavior before it shows up in results:
- A senior person is in your account, and you know who they are.
- Decisions are explained with your data, not with generic best practices.
- Reporting includes failures and what was changed because of them.
- Some recommendations cost the agency money, like pausing spend that is not working.
That last signal is the strongest. An advisor who sometimes argues against their own revenue is an advisor whose other recommendations you can trust.
Signals it is not, and the cheap-agency trap
The warning signs mirror the good signals: a junior doing the work behind the senior who sold you, dashboard links nobody explains, and every recommendation conveniently increasing scope. Each one means the fee is funding the agency's structure rather than your account.
The cheapest agency is rarely the best value. A weak operator tolerates wasted ad spend that usually costs more than the fee gap between them and someone good. When you compare quotes, compare the total cost: fee plus the waste each operator would leave in the account. That number, not the invoice, is what you pay. Ask each candidate to walk you through a real account they manage, anonymized, and listen for specifics. Operators talk about search terms and margins; salespeople talk about partnership and growth.