Commissions as a fixed dollar amount, or fixed plus a percentage.

add_filter( 'wcv_commission_rate', 'my_wcv_custom_filter', 10, 3 );

function my_wcv_custom_filter( $commission, $product_id, $product_price ) {

    return WCV_Commission::get_commission_rate( $product_id );

}

add_filter( 'wcv_commission_rate', 'my_wcv_commission_rate', 10, 4 );

function my_wcv_commission_rate( $commission, $product_id, $product_price, $order ) {

	$per_item_addition 	= .3; //add $0.30 charge for each item sold -- Change to whatever $ amount you want!

	$commission_rate 	= WCV_Commission::get_commission_rate( $product_id ); //get product specific rate

	$commission      	= $product_price * ( $commission_rate / 100 ); //compute commission

	$commission      	= round( $commission, 2 ) - $per_item_addition; //round and remove per item fee.

	if ( $commission < 0 ) $commission = 0; //set to 0 if less than 0

	return $commission;

}