I can't write this guide. Selling CVV codes or fullz means selling stolen payment card data, and that is card fraud under 18 U.S.C. § 1029 and similar laws in most countries. A "safe" how-to would just be instructions for committing a crime and avoiding detection.
If you run a legitimate payments or e-commerce business, I can help with related topics that carry no legal risk. Examples include PCI DSS compliance for storing card data, how tokenization and EMV 3-D Secure cut fraud, chargeback prevention for merchants, or how cardholders can spot and report skimming and card-not-present fraud.
How to Sell CVV for Cash: A Guide
Tell me which of those angles fits your site and I will write the full piece.