How to block search engines indexing certain AJAX actions

If an ajax call is indexed it compromises the whole purpose of the application. The cause here is that you are making your call using GET instead of POST as suggested: https://codex.wordpress.org/AJAX_in_Plugins

The right way should be along something like :

<?php
add_action( 'admin_footer', 'my_SHOP_javascript' ); // Write our JS below here

function my_SHOP_javascript() { ?>
    <script type="text/javascript" >
    jQuery(document).ready(function($) {

        var data = {
            'action': 'shopping_cart',
            'id': 16,
            'nonce': '12345',
            'type' : 'add'
        };

        jQuery.post(ajaxurl, data, function(response) {
            //YOUR CODE AFTER SUCCESS
        });
    });
    </script> <?php
}