Carders, for example Debitcarddumps, Cvv2dumps and Buyfullzonline, take advantage of software to perform the heavy lifting. Bots will try to make small purchases with a card, testing different card details. If the payment goes through, carders have a valid card. Otherwise, the bot moves on to the next car and tests new details. Paypalcvvshop, Storecc and other carders have a list of valid cards that can be sold on the black market. They're guaranteed to work if used right after validation. Once carders buy an item from an online store, it's very hard to reverse the charge. Thus, there is no chance of losing the item.