Why do people buy from you? It's a good question that deserves an answer. Ask them.
Is it location? You just happen to be in their neighborhood? They were going somewhere else and saw you? You happen to be next door to their favorite store? Location is not a good enough answer, it must have more detail. What does location mean? Is it convenience? What does that mean?
Were they referred to you? Who referred them? You will want to thank the person who referred them. Referrals are very cool.
Is is product? Do they buy from you because you happen to have a product they want or need?
Was it media? Yellow pages, Google or other search engines? Newspaper, magazine, newsletter?
The more specific you can get in why they are buying from you, the more you learn how to get more people to buy from you. It will help you to know best where to put your advertising dollars so that you actually get a return on that investment.