User blog comment:PuffPastry/Card Value ≠ PP/@comment-6015828-20130201204545/@comment-5428123-20130204083155

Pure values are not always half of card values. Lower end ultra rares like mountain hunter are often priced at about 80 to 100 in pure potions, despite having a card value between 100 to 120.

Meanwhile, cards like Flaming Werewolf are often priced at about 250 pure potions, despite often being valued at around 400 in card value.

Basically, the more expensive the card, the less likely people are willing to dish out a lot of potions to get it.