The agency model ends where your calendar begins. The lead arrives; whether it gets answered, booked, proposed, engaged, and invoiced is your problem. At most firms, that is exactly where the leak is: the marketing worked and the intake did not.
A management company owns the whole path: outbound and local presence, then the CRM, the booking flow, the follow-up sequences, the proposal and engagement-letter automation, then invoicing and AR follow-up on the work it helped land. We defend the same collections number we are paid on. Ad spend, when you choose to run ads, stays yours and passes through at cost; we are paid on the result, never a margin on media.