If you’ve ever dabbled in collectible card games — Magic: The Gathering, Pokémon, etc. — you know how quickly collections can grow. One pack turns into two. Two turns into five. Then they release some new set and… screw it, why not buy a whole box?
Card resellers have the same problem, just magnified to an extreme. People who’ve stopped playing a game for whatever reason (sometimes years prior) walk in with massive collections and just want to get rid of them. Online resellers and card stores can end up with monstrous stockpiles of unsorted cards, and going through them requires a ton of time and a wealth of ultra-specific knowledge of a game. Which cards are rare? Which ones are a bit more common, but useful enough that players would want to buy them for their decks? What are they all worth?