Write for the client who already has someone. Almost nobody arrives at an agency from a standing start: there is an in-house person, a previous agency or a relative who built the site, and the real question is what happens to all of that on the way across.
Give the audit its own page and price it honestly. "Have someone look at our ads account" is a small, low-risk purchase for a business that has been burned, and it is the most reliable way an agency wins work it would never have won by pitching.
Separate the channel pages properly. Somebody searching for paid search has a different problem, a different budget and often a different job title from somebody searching for social media management, and one page covering both reads as an agency with no depth in either.
Publish a range and a timescale even if both are uncomfortable. A business that cannot tell whether you cost eight hundred or eight thousand a month will simply not enquire, and the enquiry you lose that way is the one you would have wanted.