<?php

// Add to functions.php
function index_serialized_data( $params, $class ) {
    if ( 'item_condition' == $params['facet_name'] ) {
        $values = (array) $params['facet_value'];
        foreach ( $values as $val ) {
            $params['facet_value'] = $val;
            $params['facet_display_value'] = $val;
            $class->insert( $params );
        }
        return false; // skip default indexing
    }
    return $params;
}
add_filter( 'facetwp_index_row', 'index_serialized_data', 10, 2 );