A long time ago, I was in the market for a bit of kit - an LCD projector. We looked at a few, chose what we thought would be good for our needs, and tried to buy it.
The vendor company insisted that they send a salesman round. OK, a waste of his time and ours, but we said OK.
The saleman came, we talked a bit about what we needed, and then he went into a long explanation about all the things that go wrong with his competitor's equipment. He told us about problems that we hadn't thought of, and how his competitors failed to address these problems.
By telling us about all the problems that LCD projectors could have, which we hadn't known about, he managed to talk himself out of a sale, because I felt it was highly unlikely that his brand alone, out of all the possible brands, would have solved these problems that we hadn't known existed until this plonker told us about them.
That's one of many ways how not to sell, but there's another good one that I get all the time.
I call a company and try to do business with them. They're too busy, so I leave a message to be called back. They don't. So I call them again. Still too busy, although I'm assured that "your call is important to us", and they still don't call back, so A) clearly it isn't important, and B) they are suffering from the problem of "too many customers" so I graciously help them with this problem by not adding to their burden. And go elsewhere.