How to dynamically get eBay ItemID in your listing template
So let's assume you have a <div> tag somewhere in your listing description which you want to hold the ItemID (it's just an example to demonstrate the code):
<p class="wpl_ebay_item_id_wrapper">eBay ID: [[ebay_item_id]]</p>
Now, this is the code that I added to my listing template's header.php, which first checks if the global variable ebayItemID is already defined by eBay, and if it's not it fetches the ItemID via AJAX/JSONP and inserts it in the <div> tag above:
View script on GitHub: https://gist.github.com/wp-lab/0cd4d2fc2a6694c6b00a834b5c018ce5
To use this in your listing template, you'll need to update WP-Lister to version 220.127.116.11 or better, which adds support for the two shortcodes for admin_ajax_url and wpl_listing_id.