GrimFang501

So my question is In his scenario if he was to play on on his gf computer using his acc even though she has her own acc, and he and she trade cards back and forth between each other, would they get banned for multi accounting? How could you tell if it is not the same person or 2 different ppl? My lil brother likes to copy the games I play and I usually let him play on my PC while i'm at work. He unfortunately does not have his own PC. So how would the devs know i'm not multi accounting?