After the auction, the buyer and the seller follow a simple, guided process: won, paid, shipped, received. The buyer sees the total with the buyer's premium, shipping and VAT, chooses the shipping method and tells the seller when the payment is sent.
The experience after the auction decides whether a buyer comes back. PHP Bid guides both parties through every step, so nobody wonders what happens next.
For the administrator, every sale has a status: awaiting payment, paid, to ship, shipped, completed or cancelled. Separate admin pages for each status show exactly where action is needed.
At the end, both parties leave feedback, which builds the reputation system of your marketplace.