Add following code to the file functions.php of your theme if you want deny to your vendors to edit taxes for their products using Frontend manager dashboard.

 

if( !function_exists('yith_disable_tax_for_vendors_in_frontend_dashboard') ){
    add_filter('wc_tax_enabled','yith_disable_tax_for_vendors_in_frontend_dashboard');


    function yith_disable_tax_for_vendors_in_frontend_dashboard( $enabled ){

        $user = wp_get_current_user();
        if( in_array( 'yith_vendor',$user->roles ) && function_exists('YITH_Frontend_Manager') && isset(YITH_Frontend_Manager()->gui) && YITH_Frontend_Manager()->gui->get_current_section_obj() instanceof YITH_Frontend_Manager_Section_Products_Premium){
            $enabled = false;
        }

        return $enabled;
    }
}