One thing for sure....YOU CAN NOT GET AMERICAN CHANNELS VIA SATELLITE DUE TO FACT THAT SATELLITES WORKS ON LINE OF SIGHT TECHNOLOGY ND COVER LIMITED AREA OF EARTH. ANY SANE PERSON KNOW WHERE AMERICA IS ON THE MAP SO SATELLITES COVERING AMERICA THEIR SIGNAL CAN NOT REACH ON THE OTHER SIDE OF PLANET. ITS IMPOSSIBLE!
However as Armada suggested, you can watch American programs on many satellite's channels covering this part of the world. One of them is Hotbird (covering Europe, ME and parts of Africa and Asia) contains mostly European channels but its signal is quite weak in Pakistan specially in lower parts. and im pretty sure that is the satellite shopkeeper was talking about. you can get few channels if you put a 10-12 feet dish but you have a better option. Nilesat (covering ME and parts of Africa). its signal is accessible in lower parts of Pakistan specially in Karachi its very strong. Talk to that shopkeeper about this sat he'll guide you properly.
for the list of channels visit: