How PokéValue estimates a fair price for every Pokémon card: a ridge regression trained on ~19,000 real Cardmarket prices, with a separate computed factor for Pokémon, rarity, illustrator, set, and card type.
Every card starts from one base rate and is multiplied by a factor for its Pokémon, its rarity, its illustrator, its set, its card type, and two era-specific corrections — because what a rarity or a card type is worth has been redefined repeatedly over the game's history. The factors are not hand-picked: they are fitted jointly by a ridge regression on real Cardmarket prices, so each one is what remains after the others are accounted for.