I say that, by being gracious and spending the time, you are building a relationship with someone who, at the worst, may do nothing for you. Fortunately, they may very well, if you leave a great impression on them, recommend you to the buyer they have in mind, and may go on further to recommend you to others as well. I don't think that any opportunity to build this sort of relationship is a bad one. In fact, it might be called "networking."
Case in point; back in the late 50's my father would ride his bicycle down to the local Chevrolet dealer to look at the cars. Most salesmen would ignore him, since it was quite obvious that he was too young. One salesman though took the time to speak with my father. Usually, in a joking manner, he would go over which new Chevrolet was the best one for him, and how it could be financed. A waste of time? No. As my father approached his high school graduation, he decided to go buy his first new car. Any guesses as to where he went? In fact, other than to look at one other brand, he never shopped around for that car, he simply went to the one man who had treated him well back when there was no way he could have purchased a car.
Wear the right hat!
Bill