wp_list_table search box does not show

You must use
$list_obj->prepare_items() before $list_obj->search_box('Search', 'search') function!

Example:

                        <form method="post">
                            <input type="hidden" name="page" value="<?php echo $_REQUEST['page']; ?>" />
                            <?php $this->sales_obj->prepare_items();
                            $this->sales_obj->search_box('Search', 'search');
                            $this->sales_obj->display(); ?>
                        </form>