Change te Affiliate fee

I would like the affiliate fee to change according to the number of sales he got. So if he got more than 10 sales his flat fee would change. How would I go about doing that.

You could write a hikashop plugin implementing the onAfterOrderUpdate, check that the new status of the order is "confirmed" and if so and that a partner is specified in the order information, get the partner data from the hikashop_user table and the number of orders of the partner from the table hikashop_order and then update the partner fees in the user_params field of the user (it's serialized in the database).