Smart shopping ads are a mix of shopping ads (which show on the top of the Google search results when you look for something) and display ads (which follow you on the internet if you are a likely buyer).
I started testing them at the beginning of the year and was initially disappointed with the results - lots of clicks, no actions, not even add to cart.
Compared to my Smart Search ads which generated sales from the start, this seemed like a waste of time.
Time - that seems to be the key. I kept the ads running with a small budget (5 EUR / day) alongside my search ads and in the past few days started receiving add to cart conversions. I have also aligned the creative between the Smart Search and the Smart Shopping ads.
Now that they generate add to carts, knowing that I offer free shipping, I'm confident that they will start converting into sales.
Wish me luck!