People are the crux of the PI's business. If you dislike dealing with them, you'll have a difficult time doing private investigation. Alternatively, if you're just not very good with people, you can learn to be. Practice talking to the people you meet in the course of your day. Learn ways to engage them in conversation, and identify ways that work for you. Sometimes the soft-spoken, friendly personality appeals to people and disarms defensive postures more than the backslapping extrovert.