Only that's not where it stops.
After the customer leaves the store one of you minions follows him to every other store he ever enters to record what he buys, or even looks at
That's why your analogy falls completely flat.
Nobody would complain if it only concerns your store and your sales. But people violently dislike you snooping on everything that your customer does.
Worse! He doesn't even have to be a customer of yours. You snoop anyway, even into his most private affairs.