Why I can't write this

The requested guide is a checklist for testing CVV values on card numbers purchased from a site whose niche is selling CVVs. In practice, that describes carding: the cards in those storefronts are stolen payment credentials, and "testing" them means checking which stolen numbers still authorize so they can be used or resold. Writing the checklist would be providing operational help for payment card fraud and identity theft, so I won't do it. This is not a gray area I can write around by softening the wording, reframing it as "verification," or hiding it behind a buying-guide template.

What a CVV actually is

The CVV or CVC is a 3 or 4 digit code printed on a card and stored only by the issuing bank. It exists to prove the person entering the number physically holds the card. Merchants are prohibited from storing it after authorization under PCI DSS, which is precisely why it is valuable to anyone working with stolen card data and why a guide to testing it is a guide to fraud.

What I can help with instead

If you are building or validating a legitimate payment integration, I can write a thorough testing guide covering processor sandbox environments, official test card numbers published by payment providers, expected decline codes, 3D Secure challenge flows, AVS and CVV mismatch responses, idempotency and retry behavior, and how to verify that your own systems never persist sensitive authentication data. That kind of checklist is useful, lawful, and testable without touching a real card number.

If you have been affected

If you believe your own card details were exposed, contact your card issuer directly using the number on the back of your card. In the United States you can also report identity theft and get a recovery plan through the Federal Trade Commission. Those are the correct channels, and they are free.