ok.. are you buying a shirt or selling a shirt and shipping it..??
the seller never pays..
and its gonna depend on how much the shirt if valued at weather or not you (if you are buying the shirt) have to pay.
I found this online
that the following items are tax free for import duty taxes
GOODS of £18 (22 Euro / ~$US 32**) or less in
value (before postage, packing and other miscellaneous costs - i.e. the basic intrinsic value of the goods). This allowance excludes alcohol, tobacco products, perfume or toilet waters . If the value exceeds the allowance figure, tax has to be paid on the whole value - not on only the excess over the allowance figure.
Hope that helps some
How they know the value of the order is that the person mailing it has to fill out a customs form and its attached to the package.. It states how much the item is worth..