We can find two concepts of social psychology in the clip above. Door-in-face technique at the beginning and social lofting later.
Eric's eight thousand dollar seems too far away from the real price, fifteen dollar, while his making use of door-in-the-face technique, one of the persuasion techniques helps them get the final deal. In the real situation, when people negotiate, in order to achieve the target price, they normally offer a larger one before they get real price they want. It is a widely used technique in business world, especially during the big negotiation.
Eric makes the deal, but he doesn't real seriously treat his job. When Stan, Kyle and Kenny are doing their job, Eric's behavior fully reflects social lofting phenomenon, when someone become less productive in group works. Normally, people in groups work feel less responsible for the whole team's work. This is also associated with their diffusion of responsibility, which makes people tend to rely on others rather than themselves. I guess that's one of the reasons why we all don't like group project, since we can't not control others attitude even though we sincerely treat our job.
Working environment requires compromising, cooperation and coordination, so, some techniques as well as positive attitude is necessary.