I’m quite surprised that auctions identify users.<p>I thought it would have been “American male 20-25, likes guitars, looking at article about cars” without any ID that bidders can attach to the next auction.
They absolutely do sell your data, but only if you’re big enough and have enough money, and are discrete enough. They invited me as part of a role I played at a globo mega corp famous for being discrete, rich, and sophisticated with data to buy access to highly dimensional real time local data with amazingly detailed resolution, ability to structure and query, etc. You could do stuff like see what everyone who drives an EV is doing, what coffee shops are popular right now with liberals, etc, all in real time and with deep comparative history. It was remarkable the detail accessible on everyone everywhere all at once. It was anonymized and aggregated, so I couldn’t buy your specific data, and it was masked with differential privacy techniques - but you could certainly say they sell your data. They sold it to me.