As some one who deals with security on a daily basis, I have seen tools to prevent this.
What happens is someone advertises say 10 K cards for sale. They actually package 15 K cards in the pack, when the user gets the pack they have a robot ap that goes and makes purchases from shops that are on the internet and are known to be able to easycard fraud friendly. The robots order something quickly like a $20 cable or piece of merchandise. If its declined the card is dropped from the database.
Once all the cards are checked if the buy has close to 10 K they don't care. If less then say 8 K they get another chunk of 4 K to go at again. Until they get close to the 10 K they were promised. This is how the good groups do it. The ones who don't care just sell in chunks of 5 K to 10 K with no guarantees.
Now they also can use another system for cards to do quick transactions checks just like paypal would do to check if the card is valid. Small bump purchase then issue a refund if they want to hide from the owner of the card.
I have to monitor these "groups" as I need to make sure that none of my servers are being used in their scams. A good security guy keeps his eye on everything ! And yes we monitor IRC and other methods of chatter to see if any of our servers have been compromised.