For people who dont know what non-avs cards are here is the explanation:
AVS (Address Verification System) is used to check if the billing address provided is correct. For example even if the card details (CCnum, exp.date, 3/4 digit security code) matches the correct info and the Billing address does not macth, the card is marked as "Declined" and the order does not proccess. AVS connects to the bank and verifies the info provided.
However some banks do not allow this kind of verification, allowing the carder to input whatever billing information they want.
Q) Why are non-avs card so useful?
The answer is very simple. You can just input the shipping address as billing address when carding, means it would be same, which is a lot higher chance for the stuff to ship.
So here we go.