Simple sentence, isn't it? Pretty friggen obvious. But most people don't get it.
This was told to me by a realtor friend of mine trying to explain how she stays successful. A more detailed version would be "don't waste your time with people who aren't serious about doing business."
But I don't know how many times I have been sent out on wild goose chases, am chastised by people in other groups that they can "get a deal done thanks to their connections", and so on. One of the marks of a good salesman is knowing when a customer is playing hard to get and when they just aren't interested.
That's not to say you don't keep tabs on customers who say they aren't interested - things always change. Even my realtor friend knows that people who aren't interested now will ONE DAY buy or sell a house. The difference is knowing when to put them on the "keep tabs on" list and the "engage" list. A salesman has people in both camps, but knows the quality time is spent with the ones that are serious. The other list will hopefully feed into the engage list and needs to be managed, even if it takes years, but a good salesman knows how to distinguish between the two.