There seem to be two main types of salesmen. The first are guys who had no particular direction early in life, but who always got on well with others, mostly because they like others. They are told that they'd be good in sales, so, armed with nothing but a bachelor's degree in some nonutilitarian major, they drift into sales. This type often ends up selling paper, or lawn mowers, or insurance, or sports gear, or pharmaceuticals.
The second type of salesman is the type who prides himself on being able to manipulate and control others. He is the type who, as the old cliche goes, could sell snow to an Eskimo. And he would, too, with absolutely no qualms. Salesmen like this often end up selling big ticket items, like Mercedes or Manhattan real estate or corporate bonds or high end art.
To people like this, a customer is nothing more than a mark. Yet these are often the same people who pride themselves on their ability to build "relationships." (Their personal relationships inevitably suffer in the long run, but that's beside the point.) Such salesmen have nothing but contempt for lesser salesmen who lack their killer instinct, who don't know how to "close a deal." (For reference, see "Glengarry Glen Ross;" or visit any Wall Street bond syndication desk.)
Salesmen like this are inevitably perfectly groomed and dressed, smooth and never at a loss for words. But they always have a vaguely predatory air, and they always make you vaguely uncomfortable. One of the most discomfiting things about them is that they often have the ability to make you feel, for absolutely no good reason, slightly guilty for not buying their product.
At the same time, they're often fascinating to watch, the same way a viper is. There's something mesmerizing about their seamless act, their way of interacting with others. In some ways they're subhuman, but in others, superhuman.
Without getting too philosophical -- yes, we're all salesmen and our ultimate product is ourselves -- you have to watch out for the manipulators. If they make you uncomfortable, there's probably good reason.