I do sales calls as well and I agree with what Corey says. It's not about the selling in the end, its about the prospect being able to remember you, you being able to figure out a way to offer something of value and ensuring that the person likes it after you offer it to them. Prospects who act irritated are probably going through a rough patch, and I usually make it a point to call back in a month and check for a tone change, and more often than not, they will talk.