"After a quick evaluation of the terms of my initially scheduled lunch, I would likely let the other physician's office know that I had unbreakable commitments that day but would love to get something on our schedules as soon as possible. I would remain open to traveling and making the meeting work because it is a big client. If they were close in proximity, I wouldn't hesitate to let the physician know that I could swing by later in the day to meet face-to-face and that I'd be happy to bring coffee for us as well."

Tell the interviewer that you'll have to assess the entire situation and take all factors into consideration. For example, in the case you just had lunch last week and closed a sale with the originally scheduled doctor and today was simply a follow-up that could be accomplished later in the day, you wouldn't hesitate to take the necessary steps to cancel that lunch and work in meeting with the higher profile physician. But in the end, you'll want to ensure your interviewer understands that you would typically stick with your first commitment and then do what is necessary to ensure you meet with the high-profile physicians as soon as possible on their schedule.