At swagyard.com, shipping costs are always paid by the BUYER.
Shipping costs and return policies are determined by the SELLER. Before posting an item, do your homework on the shipping costs. Remember to consider the cost of packaging in addition to the shipping costs. All packages should be shipped with tracking information to ensure a smooth transaction.
It is at the discretion of the seller whether or not to accept returns. Therefore, buyer beware. Make sure you know what you are purchasing.
Visit usps.com. You can calculate costs, order shipping boxes, print postage, etc.
The US Postal Service has fixed rate shipping boxes of various sizes. If it fits in the box, it ships for the fixed rate.
10×13 Tyvek mailers (available at Staples, Office Max, etc). are an inexpensive option for shipping pinnies and shorts.