Answering the Unasked Question?

How important is not answering the unasked question? Should I ever tell more than what’s required?
The sales tip of never answering the unasked question I believe deserves a second thought. To a certain point, this must be a question of ethics. I understand why you would not give irrelevant or too much information to a prospective buyer in a selling situation, in hope not to say something unnecessary that would lead the buyer away. However, at what point does it become their right to know something they haven’t asked about?
My example, as mentioned in class, of this happening to me occurred this past summer when I was on the phone with a prospective customer, trying to set up a tee time for him to come play our golf course. The conversation was nearly finished when I mentioned that he can just pay the $95 rate when he shows up. He never asked how much it was. He was shocked to hear this and cancelled his tee time immediately. Did I have to tell him this? No. I botched the sale. However, having it be one of the higher end courses in Michigan, I took numerous short calls a day having people ask me how much it is to play and then hanging up the phone saying, “Oh, he** no.”
Later I pondered that call wondering if I botched the sale or not. Would if that guy showed up on the day of his round, shocked and complaining, refusing to pay out rate. Now we have not only lost that customer for good but also another one, not filling that time slot. Not to mention all the other people turned of from that guys (probable) horrible review online. Having that case play out in mind, what was the right thing for me to do?
Suppose this happens on a much larger scale. A $2.2 million contract goes through but gets revoked 4 months later after the international tech company finds that the software they were sold doesn’t work in two of their countries. These guys go on to make that known to all the other sellers’ clients, who then find themselves out of business 6 months later. Who didn’t answer unasked question that led to the company’s downfall? Not to mention a possible lawsuit there.
A Muslim man gets sold a product from a sales rep that knows the contents of its manufacturing goes against his religion. But why would this man care about that if the Muslim never asks about it and it betters him? Well, the same down spiral case happens again here as the Muslim man reacts harshly to the company.
I am not trying to give answers to situations and what to do. I simply am trying pose the thought that both sides may have negative impact. To what point does it then become an ethical question on whether to answer the unasked question? Overall, I think we ought to give a second thought in the sale of how our decision may have impact down the road. That is, of course, if we are conscious of what we are choosing to say and that something may be unasked.