The "don't want to disappoint" sales technique

Saw an interesting example of a persuasive technique used by salespeople on the second episode of Mary Portas Secret Shopper this evening. It is about 5 minutes into the episode where she is visiting various stores and getting the hard sell from various sales folk. The particular technique that interested me though was the one where the salesperson says (paraphrasing) "look, I can give your a good deal, but only today. Tell you what I'll go and start on the paperwork". This technique takes advantage of the reluctance of most people to not want to say "no" or to disappoint someone, even a stranger. It is even harder to say no when you perceive that someone has done some work on your behalf, so by disappearing to do the paperwork the salesperson is actually increasing their chances of making a sale because they are setting you up psychologically to not disappoint them once they return because they have already done something for you. Admittedly this is not going to make every interaction with a customer into a surefire sale, and if more customers are aware of the tactic then it is even less likely to work, but it work just enough to slightly increase the chances of a sale. Where there are high margins and big commissions on very few sales then this can be enough, expecially if it is a part of a whole arsenal of sale techniques.