This is from chrome developer tools, network tab
Also, would you say chrome developer tools is the lightest/most accessible way for the general public to inspect for such a thing?
EDIT: TY, schrodinger. That turned out to be a tab in Dev Tools that I just hadn't dug into before. No need to install anything!
It's actually using GET to their server and something unknown to Amazon (that would most likely be server to server and not accessible over Javascript).
Although the method on the form is POST, it has an onsubmit handler which calls the connect_amazon2() JS function (which makes a GET AJAX request on line 311) and then returns false, preventing the form from being submitted.
Yes, the Chrome Dev Tools are probably the easiest way to take a look at this type of information. I actually used Safari, but Chrome's tools are much easier to use.
The connect_amazon2() must be making the GET request.
<form id="add_products_form" name="add_products_form" onsubmit="connect_amazon2(); return false;" method="post" enctype="multipart/form-data" _lpchecked="1">