Just how much they share is a secret, but we can tell you that the listprice is 0.4% per year of shareholder assets held at Schwab, 0.35% at Fidelity and elsewhere.
For authors and publishers, the agency model provides them with greater control over the timing of their promotions and higher per-unit earnings of 70% of the listprice as opposed to 50% for the conventional wholesale pricing model.