Selling tradelines is a practice where individuals with strong credit histories add others as authorized users on their credit accounts—typically credit cards—to help boost the buyer’s credit score. This process leverages the positive payment history, credit utilization, and account age of the original account to improve the credit profile of the authorized user. Commonly used in the credit repair industry, selling tradelines can be a profitable venture for those with excellent credit, while offering buyers a potential head start in building or repairing their credit. However, it's essential to understand the legal and ethical considerations, as well as the policies of major credit bureaus and card issuers, before engaging in this market.