Full Coonditional Method

The code snippet below has 2 hooks:

1. add noindex to all GD pages
2. add noindex to some GD pages, with a comprehensive list of conditionals

It should work with most SEO plugins.

/**
 * Add noindex, nofollow robots meta directive on all GD pages.
 */
add_filter( 'wp_robots', 'gdsnippet_no_robots_all', 999, 1 );
function gdsnippet_no_robots_all( $robot_directives ) {

    if ( function_exists( 'geodir_is_geodir_page' ) && geodir_is_geodir_page() )
    {
        return [
            'noindex'   => true,
            'nofollow'  => true,
        ];
    }

    return $robot_directives;
}

/**
 * Add noindex, nofollow robots meta directive on some GD pages.
 */
add_filter( 'wp_robots', 'gdsnippet_no_robots_some', 999, 1 );
function gdsnippet_no_robots_some( $robot_directives ) {

    // Bail early if geodir_is_page() doesn't exists.
    if ( ! function_exists( 'geodir_is_page' ) ) {
        return $robot_directives;
    }

    /**
     * Combine conditionals with "||" (OR) in-between.
     * Ex: if ( geodir_is_page( 'single ) || geodir_is_page( 'archive ) ).
     */

    if (
        // GD main pages.
        geodir_is_page( 'search' )
        || geodir_is_page( 'archive' ) // All archives.
        || geodir_is_page( 'post_type' ) // Same as above, doesn't include taxonomy archives.
        || geodir_is_page( 'location' )
        || geodir_is_page( 'single' )

        // Add listing pages.
        || geodir_is_page( 'add-listing' ) // Includes edit-listing pages.
        || geodir_is_page( 'edit-listing' ) // Only edit-listing pages.
        || geodir_is_page( 'listing-success' )
        || geodir_is_page( 'preview' )

        // Others.
        || geodir_is_page( 'author' )
        || geodir_is_page( 'compare' )
    )

    // If any of the above is true, return a no-index robots meta.
    {
        return [
            'noindex'   => true,
            'nofollow'  => true,
        ];
    }

    // If not, don't interfere.
    return $robot_directives;
}

Short Snippet

The following snippet will de-index all single listing pages.
It’s possible for your developer to extend it to include others, like search, archives, etc.

add_filter( 'wp_robots', 'gdsnippet_no_robots', 999, 1 );
function gdsnippet_no_robots( $robot_directives ) {

    if ( function_exists( 'geodir_is_page' ) && geodir_is_page( 'single' ) )
    {
        return [
            'noindex'   => true,
            'nofollow'  => true,
        ];
    }

    return $robot_directives;
}