We are an agency writing about how to evaluate agencies, which you should weigh accordingly. We have also inherited enough accounts from other agencies to know what the failures look like from the inside.
Ask these. The answers are difficult to fake.
1. "What is our cost per customer, not per lead?"
The single best question. If the answer is a cost per lead with an explanation attached, nobody is measuring the thing that pays you. If it is "we can't see that," the fix is a conversion event, not a better report.
2. "Who owns the ad account?"
It should be you. If the agency owns it, leaving means abandoning your pixel history, your audiences and your learning phase. Ask to be made the owner and watch what happens.
3. "What does our pixel actually send?"
A list is a good answer. A reassurance is not. For a medical practice this is a compliance question as much as a technical one — here is the current position.
4. "Which campaign should we turn off?"
Every account has one that should be stopped. An agency that cannot name it is either not looking or not willing to reduce your spend.
5. "What would you do if we halved the budget?"
Tests whether they have a hierarchy. "We'd lose reach proportionally" is not an answer. "We'd cut X, keep Y, because Y produces the bookings" is.
6. "Have you read our ads against our state's rules?"
For medical practices in California, New York or Florida, this is a real question with a real answer. If they do not know that California requires models in ads to be labeled as models, or that New York restricts who may own the clinical entity, they are not equipped for your vertical.
7. "What is our show rate, and what are you doing about it?"
Strictly speaking, not their job. The good ones have an opinion anyway, because show rate moves cost per patient more than targeting does. An agency that treats everything after the form submission as somebody else's problem will optimize toward a number that does not pay you.
8. "What is the contract, and what happens if we leave?"
Long lock-ins exist because clients leave. Ask what you keep: the account, the pixel, the creative, the landing pages. Get it in writing.
9. "Tell me about a client you failed."
The most revealing. Everyone has one. An agency that cannot describe a failure honestly is either new or is managing you.
The one thing to ignore
Case studies with no numbers, or with numbers that cannot be reconciled. "300% increase" is meaningless without a baseline, and the baseline is always the part left out.
Ours are on the work we have done, with the actual figures and the actual timeframes, and they are thinner than most agencies' because we only publish what reconciles against a reporting sheet.
If you are interviewing agencies, take these to all of them including us. The comparison is more useful than any single answer.