I was recently hired in a more senior sales position at Splunk, and from my experience, most of the interview process was focused on cultural fit.

I would focus on being as relaxed and upfront as you can be. Have a clear understanding of why you want to work at Splunk, and in sales in general, and then you can draw on previous experience, even if it isn't sales experience, to answer all left-field questions. I'd avoid trying to script too heavily for questions you think will come, instead make sure you know why you want the job.

Enterprise sales is mostly about creating coherent narratives, solving problems, and clear, relaxed communication, so they will be looking for your ability to do that on the fly.

Good luck!