Well. I know the line is sold by many Plastic Surgeons in the office. You might check around and see the offices and talk to some of the ppl who advise pts how to use it post-op.
Have you used the line yourself and like it? That's a start!
Before your interview read all you can about their product line -- pros and cons. Look at their product ingredients as well. If you like what you find out go for the interview; it's difficult working for a firm when you don't believe in their product. Good luck.
Yes - I agree with the previous suggestions and would add - make sure that you know what their major products are and have an idea of who their major competitors are for those products.
You wouldn't be expected to know everything about the products and the markets, but should be able to carry on an intelligent conversation with the interviewer about these things. In particular, you should be prepared to ask intelligent questions which reflect more than just a casual knowledge about their business.