The process varies depending on their current demand for sales reps. In my experience, I had to attend many separate interviews. First, I interviewed with the recruiter. I was asked literally zero questions and the recruiter talked about her clothes the entire time. Then, I filled out a personality test (which is surprisingly effective - answer honestly, if you don't qualify, don't work here). After the personality test, I was told by the recruiter that they will review the results and follow up with me if everything was good. Two weeks later, after a lot of unanswered follow-up calls from me, I got a call from the recruiter saying that she would like me to come interview with the president of the company. After much preparation, I suited up and met with Doug Pitassi. He asked me which sports I played, how much money I would like to make, how I feel about swear words, and whether or not I liked to drink. I answered all questions truthfully, he approved, and directed me to have a "ride along" with one of the current sales reps. A few days later, I tagged along for an entire work day with one of the reps. Without warning, he forced me to do in-person cold calling with no training (of course I was terrible, but he wanted to see if I'd do it), I sat in on his appointments for the day (qualifying prospective businesses) and did some more cold calling. At 5pm, we returned to the office. The rep sent me to talk to their VP of sales after that (Dino Andreggen) and we discussed the results of my personality test. They were satisfactory, and he asked me more about my sports history and again asked how much money I'd like to make. We then wrapped up and he said they'd call if they were interested. The next day, I got a call from the Branch Manager of the branch they wanted me to work for. He is a great guy, asked me what frustrates me, if I'm a quitter, asked me about my previous history (they prefer no experience), and some other questions about my personality and interests. He then sent me to interview with one of the field sales managers. I had a very awkward and strange interview with this guy (I could tell he didn't like me) and we ended after a couple questions. I was then told that they'd call if they were interested. At this point, I figured I blew it because of my terrible interview with the field manager, but another day later, a different field manager called me in for another interview. Apparently he was on vacation, otherwise I would have met with him the previous day. We basically just talked about sports and he asked me when I'd like to start. With much relief, I accepted the job and started a week later.
All of this being said, I've heard that everyone else's interview process was much easier than mine. I was told years later that they were surprisingly full for a sales bullpen when I was hired and that they were probably stalling to wait for someone to quit before I was hired.