You can answer this question in numerous ways. But to make your answer effective, you should think of an answer that will show your strong points as a salesman. Make sure to cover your own traits that are important to sales. Here is an example.
Short Answers
I like sales because I like talking with people and I'm good at making people feel comfortable.
I enjoy sales because it requires strong communication skills and that's one of my strong traits. I like the challenge of making a sale and I feel good whenever I make a good sale.
I like sales because it fits my personality. I enjoying working with all sorts of people and I like to provide great customer service by answering questions about products professionally.
Long Answer
I've always liked sales. I enjoy working with and talking to people. I'm good at making people comfortable and I also like the challenge. In the past with my friends, I heard comments frequently that I would make a good salesman even before I got into sales. So basically, I like sales because it fits my personality and I really enjoy it.
This is a simple short answer. Not everyone can be a salesperson. They need to have the right personality such as good communication skills. You don't have to have a great answer for this question. But the most important aspect is showing that you enjoy sales.