The Observer pays attention to psychologists like Robert Cialdini [Influence: The Psychology of Persuasion] and Robert Levine [The Powers of Persuasion] studying persuasion skills.
Sarah Wilson writes (excerpt):
• Reciprocity is one of the most powerful tools of persuasion [give someone something before trying to to persuade them to give something back] . . . .
• Having something in common with the person you’re trying to persuade gives you an advantage [person’s name in common with you/your family] . . . .
• Raising or lowering anchor points is another popular sales technique [publishing higher price and dropping as sign of bargain while still getting your price].
• Once someone has agreed to a deal, they’re unlikely to go back on it, even if the terms of that deal change [commitment and consistency].