If you like what you are doing, this will come naturally. This is what everyone thinks you are doing by running the business. This is why they come to you. You are an expert in your field. You will have to let people know, and give speeches, hold workshops, teach a class, etc. The by now famous E-Myth refers to the fact that everyone sees the small business owner in a sea of bliss doing what he loves. You will need to have this skill, if not immediately, then develop it along the way. Don't buy the business in the first place on this alone, however, unless there are people out there besides your mother who agree you are an expert.
If being an expert in your field is your only business qualification, if you don't meet the other criteria - you could be in for trouble.