Originally posted by Guy Betsy:
the airlines can have the autority to decline you borading in USA when they check your passport and don't see a stamp in say, Bogota, where you might have bought your ticket from.
A lot of countries no longer stamp passports. They either scan them or enter your details into their computers. But I am sure that airlines have easier ways of checking whether the actual flight commenced from the country where the ticket was purchased from or not.