If you are talking to two or three suppliers before handing over an account, their pitches will probably sound alike. The differences come out when you ask a handful of direct questions and expect written answers before any quote. Whether the supplier calls itself a PPC agency, a paid search specialist or a digital marketing firm, these questions still apply.
Whose name is the account in? It should be yours, with the agency given access. When an agency runs your ads from an account it owns, leaving can mean losing years of history, conversion data and everything the bidding has learned.
How will you check our conversions? Relying on whatever Google reports is not an answer. A careful supplier will explain how it will compare the conversion column with your enquiries, calls or orders, and what it does when the two disagree, which they often do.
How is the fee worked out? A fee taken as a share of ad spend rises every time the budget does, whether or not results improve. A quote for the work itself, with the scope written down, keeps the agency's interest tied to what the spend brings back rather than how much of it there is.
Who will actually work on it? Ask who logs in to the account week to week, and whether the same person writes the report you receive. In some agencies the person who wins the account is not the person who runs it.
What happens in a bad month? Every account has them: a competitor raises its bids, a season ends, a website update breaks a tracking tag. You want to hear how the agency would spot it and tell you, not an assurance that it will never happen.