Unfortunately, I couldn't find an example of this type of ad. However, it's used just like the sales closer, preferably by only targeting people who landed on your checkout page and then did not complete their order.
This would be instead of people who merely landed on your product or sales page. The ad would show the product, plus say something like, "Oops, you still have an item in your cart."
Hopefully, enticing them to come back and complete their order this time.