The short answer
Choose a diagnostic when you still need to decide what to fund. Choose execution when the demand, conversion path, operating owner, and economics are already established.
A marketing agency is useful when the company already knows which path to operate. A market diagnostic is useful when demand, positioning, compliance, margin, or local operations remain uncertain. The diagnostic decides what to fund; execution operates the agreed scope.
Compare providers by how far they connect discovery, trust, inquiry or product page, conversion, support, repeat purchase, and revenue measurement—not by the number of posts or campaigns promised.
A useful diagnostic leaves demand evidence, readiness gaps, channel economics, localization requirements, 90-day priorities, and stop conditions. It should remain valuable even if no execution contract follows.
If demand and conversion are already proven and an internal owner exists, execution may be the immediate need. Otherwise, a paid independent diagnostic reduces the risk of buying channel activity before the commercial path is ready.