One of the cliches of startup life is “fall in love with the problem, not the solution”.
One of the implications of this philosophy - if followed to its logical conclusion - is to understand that the problem likely starts further upstream than you imagine; and goes further down stream than you imagine.
Consider that, once your initial wedge in the world begins to gain traction, you have an opportunity to expand into logical agencies up and down (and across) the value chain.