That's the precipice of the argument though, right? It's not illegal to observe interactions that you witness, or take notes about customers you saw shopping your competition.

You could even hire someone to wander around your competing stores and take lots of notes about the people they saw. "Red shirt guy shopping around for slim fit pants". Unlikely scenario, but legal to do and to use that information.

My whole thing is - what makes the scenarios different enough that one is prohibited and one is allowed? Certainly if we told folks they must forget their observations about others upon request, that would face some baseline rebuttal about their own autonomy.