This is a potentially fraught situation, because the patient has made up his mind that he needs something, like an expensive test or an antibiotic for a viral URI, and won’t be satisfied until he gets it. You explain your medical thinking, and he doesn’t accept what you say. The patient can perceive your refusal as intransigence, as your not caring or wanting to be bothered, or any number of things that are untrue. This approach can work:

Let’s just stop for a moment. You know, the easiest thing in the world for me to do would be to simply write the prescription, and you’d get what you want and walk out happy. Quick and done, no sweat off my back. Instead, I’ve just spent all this time explaining to you why I don’t think it would be in your best interest medically. I’ve risked pissing you off, making you resent me, and maybe even causing you to leaving my practice, when all that could be avoided in thirty seconds just by giving you a prescription. But I didn’t do that because my sole interest here is what, based on my knowledge and thirty-five years of experience, I think would be medically best for you.