At first, you probably will say "Yes!". It's sort of an eating-your-own-dogfood thing. I think the opposite is true. Chances are, you're not good at your own marketing. As Dilthey taught us, understanding a person requires looking at that person's expressions—their works. Most people think that these works mean what the person intended them to mean. It's just a question of uncovering the (likely hidden) intention behind the work. Yet, one of the central ideas of contemporary philosophy is that the author is dead. Once the work is complete, it is released into the world. Out in the world, the work takes its place in a web of meaning—meaning that likely has little to do with what the author "intended". In other words, authors do not have any special insight into the meaning of their work. So, what does this mean for doing your own marketing? Naive authors think that they are the best persons to interpret their work. In reality, they have no special advantage. Indeed, thinking that they have a special advantage actually makes them much worse at such interpretations. It is the same with marketing companies. If a company fails to understand that it's theoretically no better at doing its own marketing, it will do a worse job at marketing than for its own clients. Only when a marketing company recognizes that it has no special insight into its own meaning (simply for being the same company) does it have a chance to do a good job on its own marketing. And this is a rare thing. So for most marketing companies, I'd say: don't do your own marketing!