Auto-tagging for free listings is now available in your Merchant Center account.
With auto-tagging, after someone clicks your free product listing and free local product listing, auto-tagging adds a bit of additional information — a parameter called “result id” — to the URLs people click through.
When used together with a third-party web analytics tool (like Google Analytics), this will allow you to see how effectively your free listings and free local listings lead to valuable customer activity, such as purchases.
What you need to do
You can enable auto-tagging in your Merchant Center account under "Conversion settings"