answer:Promo cards are often fairly rare and thus worth a bit more. Like most things, card prices are determined by supply and demand. Cards that are great in-game tend to be more in demand, and those of increased rarity, by definition, have a smaller supply. Often the rarer cards are also the most powerful in-game, so they get a double-boost in price. Most CCG games have price lists that tell you the current price of each card, but I cannot seem to find a current one for Pokemon, at least not in the few minutes I have before I have to go. I’ll see what I can find later; if yu don’t hear back from me, assume I didn’t find one. In the meantime, read this