For Sales positions there is a three or four interview process. The intial phone screen by HR, meet with District Sales Manager, meet with Director of Sales and/or GM. After the interview with the District Sales Manager, you will take a personality profile called Caliper. It really is used to determine if you would like the job. Sounds crazy, but answer the questions honestly, really if you aren't going to like the job you should know now.
The interviews are suppose to follow a format with Interview Guides that are published as "A","B", and "C". Technically, you should get a different interview guide at each interview and the three interviewers compare your answers. If they actually followed the process, it might work. Most of the time the interviewers make up their own questions or have favorite ones they ask and leave off others. Lots of situaional questions, "Tell me about a time..." and it is important you follow the STAR method for answering them. The more specific you can be the better.
Dress well for the interview, suit and all! They sell image and they take it seriously. You will not interview with a single person with a self image issue, if anything they are arrogant. They are tough and driven people and value hard work above just about anything else. Don't let the polite midwestern facade fool you, they eat their young. Take notes and do your research on the company so you can ask good questions.