You become friends with whoever you are going to trade with first. Then you have them put the card up on the auction block for the price you agree on and buy it. So if you want to trade card for card you both but them up for cheap (100 coins). Make sure you change the auction setting at the bottom to friends and what position you want, that way it will pop right up and you don't have to search for it and run the risk of it being "sniped" by someone else. Be careful who you do this with. There are a lot of scammers out there!!!