gistfile1.txt

$enquiry_form_output_already = false;
add_filter( 'propertyhive_viewing_request_show_fields', 'hide_show_form_fields' );
function hide_show_form_fields($show)
{
    global $enquiry_form_output_already;

    if ( $enquiry_form_output_already === false )
    {
        // first one. Show fields
        $enquiry_form_output_already = true;
        return true;
    }

    return false;
}