Here’s how it really works: GPS captures device IDs as people enter your store. Then the platform matches those IDs back to the IDs of those who saw your ad through your cross device identity graph. This gives you a transparent answer on if your ads actually worked to usher in more foot traffic. By evaluating your exposed visit rate to the unexposed visit rate folks that came into the store without seeing your ad, that you can easily calculate the lift from your ads.
Plus, many platforms allow you to send panelists who visit your store a quick survey to extra examine product cognizance and purchase intent among exposed and unexposed users.