At some point most marketers end up choosing an agency rather than working at one. It is a skill nobody teaches, it is usually done under time pressure, and the standard advice is to look at case studies and ask for references. Both of those are the parts an agency has prepared.
What follows is a set of checks that are harder to stage, in the order they are worth doing. It is written as a teaching piece rather than a buying guide, so it includes what a good agency's answers actually sound like.
Check one: can they describe your problem before pitching
Ask what they think your main constraint is, before they present anything. A strong agency will have looked and will say something specific, including something you would rather not hear. A weak one will restate your brief back to you and move on to their credentials.
This single question sorts most shortlists, because it separates the agencies that did an hour of unpaid thinking from the ones that did not.
Check two: who actually does the work
The people in the pitch are frequently not the people on the account. Ask directly who will be doing the work week to week, how many other accounts they carry, and what happens when they leave.
The answer to be wary of is a large team structure with no names in it. The answer that is reassuring is a small number of named people and a candid statement about their capacity.
Check three: what they will not do
An agency that says yes to everything is either much larger than it appears or has not thought about it. Ask what work they turn down and which channel they are weakest in. A real answer here is one of the strongest signals available, because it costs them something to give.
Check four: the reporting question
Ask what the monthly report contains and ask to see a real one with the client details removed. What you are looking for is whether it reports on outcomes or on activity. A report full of impressions, reach and posts published is an activity report, and it can stay green for a year while the business gets nothing.
If you are not confident judging that, the five numbers worth insisting on are set out in marketing analytics for beginners, and the shape of the underlying journey is explained in the marketing funnel explained for beginners. You do not need to run the campaign to check whether the reporting is honest.
Check five: the responsibility that does not transfer
This is the one that is routinely missed, and it is not a matter of taste. When an agency runs influencer, affiliate or referral work on your behalf, the disclosure obligations attach to you as the advertiser, not only to them.
The United States Federal Trade Commission puts it flatly in its endorsement guides: your company is ultimately responsible for what others do on your behalf, and advertisers are expected to have reasonable programmes in place to train and monitor members of their network. The guides also state that a connection between an endorser and a marketer that a significant minority of consumers would not expect, and that would affect how they judge the endorsement, should be disclosed.
Rules differ by market and the FTC's writ does not run everywhere. The principle it encodes is the useful part: hiring an agency moves the work, not the accountability. So ask what their disclosure practice is, ask to see how a paid post is labelled, and ask who checks it. An agency that has never been asked this will tell you so by how long it takes them to answer.
The same logic applies to reviews. Google's own Business Profile guidance is unambiguous that offering incentives in exchange for posting, changing or removing reviews is treated as fake and misleading content and is strictly prohibited. If an agency proposes a review campaign built on incentives, that is your listing they are risking.
Check six: the contract's exit
Read the notice period, and read who owns the accounts. The recurring damage in this market is not a bad campaign, it is an agency that built the ad account, the pixel, the analytics property and the page under their own ownership, so leaving means starting again with no history.
Every account should be created under your ownership with the agency granted access. This is free to arrange at the start and expensive to fix later, and an agency that resists it has told you something important.
Check seven: who is really deciding on your side
Before you compare proposals, be clear about who internally has to agree, what each of them is worried about, and who can say no late. Evaluations fail more often from an unmanaged internal group than from a bad shortlist. Our colleagues at BDG Labs describe that group and its behaviour in the B2B buying committee, and reading it from the buyer's side is a fast way to notice you have skipped somebody.
Honest limits
Two things this process cannot do. It cannot tell you whether the agency is good, only whether they are careful and honest, which correlates but is not the same. The only real test is three months of work, which is why a short paid pilot with a defined deliverable beats a long first contract.
And it cannot compensate for an unclear brief. Most disappointing agency relationships start with a client who did not know what they wanted and an agency that agreed to it anyway. If you cannot say what would count as success in twelve weeks, fix that before you shortlist, and the ordering of that thinking is in digital marketing for business owners: what to learn first.
Finally, if you are learning this in order to work at an agency rather than hire one, the checks above are a fair description of what a good client will put you through, and preparing for them is a reasonable way to decide what kind of agency to join. Understanding what the delivery side actually involves is covered in what is media buying.