Once someone has agreed to buy your listed item, or has accepted your donation, it is your responsibility to set up an arrangement between the two of you to exchange the item for any monies. Progressive U is not participating in the exchange of these items - only giving you a place to list them.
Your method of shipment and, if applicable, your method of payment is up to you to set. If you prefer the U.S. Postal Service over FedEx...then it's your prerogative. If you wish the buyer to pay you via online means, such as PayPal - that is also up to you. Please make sure your ads list these criteria.
