Reg BI has four obligations: disclose the capacity, fees and conflicts; exercise reasonable diligence, care and skill; establish policies to identify and address conflicts, eliminating sales contests and quotas tied to specific products; and comply with documented procedures.
The care obligation has three parts that matter to active traders. A recommendation must be reasonable for some investors, reasonable for this particular one, and reasonable as a series, which is the hook used against churning and excessive options recommendations.
It is a recommendation standard, not an ongoing duty, and it stops short of the fiduciary-duty owed by advisers. Self-directed trading that a broker did not recommend sits outside it entirely, which is why order-entry-only platforms lean hard on that distinction.
Related: suitability, fiduciary-duty, form-crs, churning, broker-dealer