That this happened to me, the rare consumer who reads privacy policies and is constantly on the lookout for creepy data collection, demonstrates what little hope there was for the typical car buyer.

Harry Brignull, author of “Deceptive Patterns: Exposing the Tricks Tech Companies Use to Control You,” said: “In these sorts of agreements, they need to be very clear about the true function of it.

Ms. Barker said G.M.’s terms and privacy statement allowed the company to share information with “third parties” — legalese that people agree to on the first screen the salesman was instructed to show us.

Kate Aishton, a lawyer who advises companies on data and privacy practices, deemed the process poorly designed for obtaining actual user consent, particularly since it takes place in a high-pressure sales environment.

A new car, like mine, has hundreds of sensors, the former employee said, so even just a 15-minute trip creates millions of data points, including GPS location — all of which is broadcast in near real time to G.M.

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