Sure, and often trade against their clients, but for their own financial interest.
Or convince their clients to use their tax deferred accounts to buy a high-commission tax deferred insurance product or annuity that underperforms a low-cost index fund. I’ve even seen brokers use tax deferred retirement accounts to buy over-priced tax-free government bonds that the brokerage house has underwritten. There is no legitimate investment reason for any honest investment advisor to recommend tax free bonds within a tax deferred retirement account.