GST is to be paid to the final destination (if there is one). If you paid GST to the country of purchase (eg US, UK), you should try and reclaim it. Depending on your mode of purchase/shipping, you may be able to reclaim it back.
So if you purchased something from Amazon US, and had it shipped to Pakistan directly, chances are you will not pay any tax to US govt. Now when the parcel arrives in Pak, you will probably be liable to pay some taxes to Pak Govt depending on the value of the good (and frankly the mood of the Pak Custom officers :P).
If you asked a friend to purchase something from Amazon US to deliver it to him in Florida and then bring it to Pak in his suit case, most likely he will be pay 6% tax he has to pay to his state. Since, he is "smuggling" the items to Pakistan in his suitcase, he will most likely escape the Customs Duty.