A piece of advise, if your item is small, make sure that seller label its price below 10 dollars. In PK, up to 1000 rupees package is exempted from custom duty.
Another piece of advice, use China Post Registered Airmail or Signapore Post. Your package will reach you earlier and guaranteed. 'China Post Ordinary Small Packet Plus' may get lost somewhere even in China or if it ever reached you, you would be 1 or 2 months older than when you ordered it. (if you think china is 100% corruption free you are wrong. There are thieves working at clearance/customs/shipment who will steal your unregistered product)