From what I understand they often start with some sort of brainwashing, they are also taught weird beliefs like "every time a customer says no the odds of the next customer saying yes will increase".
I guess it will depend on what the product being sold is, enterprise software is probably somewhat different to timeshares or double glazing.
It is worth bearing in mind though that some of the best salesmen throughout history have probably been people who were knowingly selling scams.
