Buying and selling doesn’t have to be a zero sum game of winners and losers (but it’s often perceived that way). One behavior I’ve observed which reinforces the image of “the dark side of selling,” as you call i,t is not enough listening. Most salespeople, (myself included), have a difficult time of pausing their talk track to ask questions. And even the sales people who do ask questions tend to ask self-focused questions rather than other-focused questions. Sales people who develop habits to overcome this pattern can become amazingly successful, in my experience.