If EA really is buying cards, that's the only factor that matters. They can then set the prices wherever they want them. Sure, they inject money to the market through the seller when they buy them, but that money is reused by the seller to have to buy at an elevated price too so its a wash. They only need to buy enough to assure the new postings are higher. Meanwhile, EA still takes 10% on every transaction.
If EA really is buying cards, that's the only factor that matters. They can then set the prices wherever they want them. Sure, they inject money to the market through the seller when they buy them, but that money is reused by the seller to have to buy at an elevated price too so its a wash. They only need to buy enough to assure the new postings are higher. Meanwhile, EA still takes 10% on every transaction.