Agency: Custom work, hourly or project pricing, scales with headcount. Productised service: Standard offer at a fixed price, e.g. "Webflow site in 14 days for $4,800." Consulting: Hourly advice, no delivery, scales with reputation.
Productised services are dramatically easier to sell, deliver, and scale than custom agency work. The reason most agencies stay agencies is that productising requires saying no to revenue — and that's psychologically hard.