private function set_customer( $row ) {

    global $wpdb;

    if( ! empty( $this->field_mapping['email'] ) && ! empty( $row[ $this->field_mapping['email'] ] ) ) {

      $email = sanitize_text_field( $row[ $this->field_mapping['email'] ] );

    }

    // Look for a customer from the canonical source, if any
    if( ! empty( $this->field_mapping['customer_id'] ) && ! empty( $row[ $this->field_mapping['customer_id'] ] ) ) {

      $canonical_id = absint( $row[ $this->field_mapping['customer_id'] ] );
      $mapped_id    = $wpdb->get_var( $wpdb->prepare( "SELECT customer_id FROM $wpdb->customermeta WHERE meta_key = '_canonical_import_id' AND meta_value = %d LIMIT 1", $canonical_id ) );

    }

    if( ! empty( $mapped_id ) ) {

      $customer = new EDD_Customer( $mapped_id );

    }

    if( empty( $mapped_id ) || ! $customer->id > 0 ) {

      // Look for a customer based on provided ID, if any

      if( ! empty( $this->field_mapping['customer_id'] ) && ! empty( $row[ $this->field_mapping['customer_id'] ] ) ) {

        $customer_id = absint( $row[ $this->field_mapping['customer_id'] ] );

        $customer_by_id = new EDD_Customer( $customer_id );

      }

      // Now look for a customer based on provided email

      if( ! empty( $email ) ) {

        $customer_by_email = new EDD_Customer( $email );

      }

      // Now compare customer records. If they don't match, customer_id will be stored in meta and we will use the customer that matches the email

      if( ( empty( $customer_by_id ) || $customer_by_id->id !== $customer_by_email->id ) && ! empty( $customer_by_email ) )  {

        $customer = $customer_by_email;

      } else if ( ! empty( $customer_by_id ) ) {

        $customer = $customer_by_id;

        if( ! empty( $email ) ) {
          $customer->add_email( $email );
        }

      }

      // Make sure we found a customer. Create one if not.
      if( empty( $customer->id ) ) {

        if ( ! $customer instanceof EDD_Customer ) {
          $customer = new EDD_Customer;
        }

        $first_name = '';
        $last_name  = '';

        if( ! empty( $this->field_mapping['first_name'] ) && ! empty( $row[ $this->field_mapping['first_name'] ] ) ) {

          $first_name = sanitize_text_field( $row[ $this->field_mapping['first_name'] ] );

        }

        if( ! empty( $this->field_mapping['last_name'] ) && ! empty( $row[ $this->field_mapping['last_name'] ] ) ) {

          $last_name = sanitize_text_field( $row[ $this->field_mapping['last_name'] ] );

        }

        $customer->create( array(
          'name'  => $first_name . ' ' . $last_name,
          'email' => $email
        ) );

        if( ! empty( $canonical_id ) && (int) $canonical_id !== (int) $customer->id ) {
          $customer->update_meta( '_canonical_import_id', $canonical_id );
        }

      }


    }

    if( $email && $email != $customer->email ) {
      $customer->add_email( $email );
    }

    return $customer->id;