Possible types of delivery:
FIFA 18/17 Player auction
Here you sell one of your players to the price of the maximum price range. This corresponds to the amount of coins of the order.
Here you give your account data and the coins transfer will be taken over completely for you by the coins seller.
You receive an account on which the desired amount of FIFA coins is deposited. After that you can take over the transfer yourself.
FIFA Auction house
You list a worthless player into the auction house and the seller buys this player. This way the coins are transferred.
Note: after clicking on the "purchase" button, you will receive detailed information about every single type of delivery. There it will be explained step by step which conditions have to be fulfilled.