It's highly unlikely that they are going to provide you with a sample of the code, so really what you need to figure out is how you can answer your questions without seeing the code. You're trying to make sure that they value good coding practices, so ask them about that.
What sort of source control do you use? How does the team report bugs? Do you conduct peer reviews on code? How do you maintain legacy code over time? How do you keep your team members up-to-date on the best coding practices and techniques?
Questions like these should help you understand how much value the company puts on maintaining quality code over time.