Salesfolks know that people don't want to be upsold , but that only makes them try harder. For people who work on commission , getting some extra cash in their paycheck at the end of each month is irresistible. And all they have to do is sell their customers add-ons that they don't really need, like insurance for expensive electronics. Just anecdotally, there are two types of people: those who never break their devices, and people who can't go a month without cracking their iPad screen wide ope…