I spent a lot of time in consultancies and started one myself, I'm not tptacek but here's my two cents.
Does the buyer see you as a commodity? How hard is it to find someone else to do what you do?(as defined by the customer not you) Can you differentiate yourself from competitors?
I think it really comes down to establishing a brand. And the problem is if you can't establish a brand you can't charge enough to fund growth (and at the beginning charge enough to give you time to grow the company).
A company with a brand can charge 2-3x their labor costs. A company without one can maybe charge 25% more than their labor costs and this puts you in the classic consultancy spiral where you spend so much time working for your business you don't have enough time to work on your business.