Authorized user trade lines work by adding someone as an authorized user to an existing credit account. This means the authorized user will have the account’s positive payment history and credit utilization factor reflected on their credit report. You become an authorized user on someone else’s credit account when you buy tradelines. The credit reporting agency includes the primary cardholder’s record in your credit report. This allows you to enjoy their excellent credit history. It helps improve your credit score based on credit scoring models. Once you are an authorized user, the account’s history will appear on your credit report. This includes factors such as the length of account history, payment history, and credit utilization. All of these factors can have a positive impact on your score. As an authorized user, you do not have any legal responsibility for the debt associated with the primary tradelines. This means you are not liable for missed payments or outstanding balances.