Guarantees & Sharing in Accounts
Two flat prohibitions: a rep may never guarantee a customer against loss or promise a result, and may not share in a customer account's profits or losses except with prior written authorization from both the firm and the customer, and in proportion to the rep's own contribution (proportionality waived for immediate family).
Related conduct rules: reps cannot borrow from or lend to customers except under narrow firm-approved programs (or with family/financial-institution customers), and paying commissions to unregistered persons is prohibited.