public function increase_ticket_sales_by( $ticket_id, $quantity = 1 ) {
		// Adjust sales.
		$sales = (int) get_post_meta( $ticket_id, 'total_sales', true ) + $quantity;

		update_post_meta( $ticket_id, 'total_sales', $sales );

		// Adjust stock.
		$stock = (int) get_post_meta( $ticket_id, '_stock', true ) - $quantity;

		// Prevent negatives.
		$stock = max( $stock, 0 );

		update_post_meta( $ticket_id, '_stock', $stock );

		return $sales;
	}