Does participating in social media get you more customers?

[Red Flower]

I've been doing the social media posts for a museum for about 9 months as a volunteer.
I recently went to a job interview to do freelance social media for a non-profit. The non-profit employer asked me if the social media at the museum resulted in more visitors, customers etc..
I didn't know the answer but to the best of my knowledge the social media has not resulted in more customers. What can I tell a potential employer about how social media will increase his business? Is it a falsehood that social media increases your business?
I can tell a employer that social media will increase awareness of his business but nothing more. How to you handle this question at an interview? How can I convince them that it's worth paying a social media person?