Bit of a dangerous thread to comment on, but I own a small agency and while ultimately billable hours is how we make our money, the overhead of getting new customers is also incredibly high. The key way for us to be successful is to build long-lasting relationships where each side feels they continue to their money's worth.

We mainly work for small and medium-sized businesses so typically it wouldn't fall exactly under the radar if we're not producing.

That all being said, I've been on the other end of this with agencies and freelancers and I would concur that you should treat these relationships as adversarial until trust is built.