I don’t think anybody claims that you need consent to do the equivalent of displaying “other products you may like”. The customer entered the store willingly, a

I don’t think anybody claims that you need consent to do the equivalent of displaying “other products you may like”. The customer entered the store willingly, and what you describe is quite literally the job of a shop assistant. The need for consent would come if the assistant were to record the entire conversion you have with the customer, and send it to Facebook or Amazon in exchange for money.