If you have prior sales/customer service experience, describe your experience by giving a brief overview of your resume. This question offers a great opportunity to reveal sales and customer service experiences that may not be included in your resume. Give examples by using your previous work experience, whether you worked in a retail environment, or related. Be sure to provide your interviewer with your sales-related accomplishments as well.
If you do not have experience as a Sales Associate, be transparent about this fact. Rather than leading with an 'I do not have...' statement, try leading with what you do offer. Perhaps you are a very social person and find it easy to speak to strangers, or if you are a friend who constantly introduces your friends to the hiring company's products. Even if you don't have past sales/customer service work experience, you should be able to demonstrate that you are driven and that you have the characteristic and transferable skills needed to be successful in this Sales Associate role.