Yes! In fact, up to this point you have been, that is how you have the customers you already have. However, for many companies, focusing on marketing isn't easy. It tends to put on the back burner or settle for just throwing darts at a dartboard and hoping you hit something.
Clients are not going to walk into your office and ask for your services unless they know who you are, what you do, and they have confidence that you can deliver on your promises. More importantly, your prospects want to know why your product or service is of benefit to them, and how you are differentiated from your competitors.
To get those facts communicated your business needs an effective, well thought out and executed marketing plan. Most businesses understand the need for a strategic marketing plan, but few understand what it is or how to implement one.
So although you can market yourself, hiring a marketing expert pays for itself with the ROI you receive due to their knowledge and experience.