Final answer:
Registered representatives must keep detailed records for each existing customer account, including personal identification, registration documents, agreements, profiles, suitability information, and transactional records, for regulatory compliance and service integrity.
Step-by-step explanation:
A registered representative must keep various records related to each existing customer account, as mandated by securities regulations. These records typically include the customer's personal identification information, account registration documents, written agreements between the customer and the firm, account profiles, suitability information, and records of transactions and communications regarding the account. Keeping these records is crucial for regulatory compliance, customer service, and maintaining the integrity of financial markets. For example, transaction records help in monitoring for suspicious activity and are essential during audits or disputes. Maintaining a detailed account profile helps in ensuring that investment recommendations align with the customer's investment objectives and risk tolerance.