Various forms of financial planning was what came to mind. The predecessor to robo-advisers. The guys I know that are really killing it in this have a few dozen

Various forms of financial planning was what came to mind. The predecessor to robo-advisers. The guys I know that are really killing it in this have a few dozen clients investing several million each with them. Their commissions from this sort of thing are large enough that they only need to have this occur a couple times a year to be well into six-figure territory.