I don't have time to discuss this right now?
Sit down! ignore him / her! - then go into your sales presentation, but add this sort of opening general interest phrase:
Say to the speaker/ buyer. You remind me of Betty Butters, she was always in a hurry, always anxious to see what we could do for her, but I told her " Look Betty, this is too serious a matter to be rushed, okay your going to save money, all right I know you want this, but for Gods sake slow down, I want you to look at this carefully, bring your Floor Manager / Personnel officer person in here and lets find out how we can help you, now then tell me slowly what you can see that I can't in this product or offer, give me some input, and when he comes in we'll ask him/ her what they think,