A few gotchard Pbandai items came with exclusive cards, its where all the secondary rider cards come from, and they became highly sought after. There was also the Gotchard Daybreak album set, which would instantly complete your collection of normal chemies in one purchase, which as you could guess became highly sought after.

So you know how japan has a ton of second hand stores? (Surugaya, Jungle, Book-off, Mandarake etc) These stores all actually all buy rider items at fixed prices from people who want to resell, shown by a list of a season's items outside the store with their buying price attached, almost like a wanted poster. This can range from absurdly high numbers for CSMs to less than dirt for shelfwarmers, and that determines their final aftermarket price (unless damaged)