Regulation Best Interest (Reg BI) requires financial advisors and broker-dealers to provide disclosures regarding their fees and services, to consider costs when recommending products to clients and to disclose or eliminate any conflicts of interest.
Reg BI mentions 529 plans but does not distinguish between advisor-sold and direct-sold 529 plans.
Even though a direct-sold 529 plan is not sold by a financial advisor, unlike an advisor-sold 529 plan, Reg BI still applies when a financial advisor recommends that their client purchase a direct-sold 529 plan.
A financial advisor should not normally have any financial interest in a direct-sold 529 plan nor a conflict of interest in recommending a direct-sold 529 plan. Nevertheless, they are making a recommendation of securities to be bought by their clients and therefore Reg BI applies.