tipster

One who sells tips or information, as to bettors or speculators.

A person specially employed in furnishing tips or secret information to persons interested, for betting or speculative purposes, in the issue of horse-races, the rise and fall of stocks, etc.: distinguished from a tout, who may be in the tipster’s employment.

One who makes a practice of giving or selling tips, or private hints or information, esp. for use in gambling upon the probable outcome of events, as horse races.

one who sells advice about gambling or speculation (especially at the racetrack)