Most people arrive knowing the symptom rather than the service. Enquiries are down, the site looks nothing like the business it now represents, or the ad budget is spending without anyone able to say what it bought. Any of those is a fine place to begin a conversation.
If you would rather work it out yourself, every page below states who the service suits, when it is the wrong thing to buy, and what moves the price. That middle one is the section most agencies leave out, and it is usually the one worth reading first.
Nothing here is sold on a rolling retainer you have to give notice to escape. Every engagement is a written scope with an end date, and the services below combine into one of those rather than into four separate relationships you have to keep managing.