I don't think there are shopping bots. It's just some random bots, that keep following links. If your theme has "Add to Cart" links, then they will follow it. Most of the time it's the button in category view. Those bots ignore "no-follow" and "robots.txt". Blocking them will not help, because there are thousands, if not millions of them. The only way to stop it, is to remove Add-to-Cart Buttons that are defined as links or replace them with a JS based button.