Why the focus on advertisers and salespeople? I mean, if you're just talking about extending 'useful' social interactions, policemen do that too. So do company managers and military officers. There are lots of lines of work where people interact with a large number of people on a daily basis. Drug dealers would be another example. Yet such professions need not act in a way that is psychopathic (except maybe drug dealers, but they, too, often build friendships and trust with their clients).