I don't know if it is still the case, but when I sold advertising in radio and in television, and speciality ad products, all political ads had to be paid for upfront, that is before they ran or were produced. The speciality products also had to have a union label. I think pay upfront was done to make sure even the losers had paid their advert bills, esp. in small markets where the mom and pop stations couldn't afford to write off bad debts.