Well, pricey hardware, at least.
> In the case of google they sell you
No, they aren't in the slave trade; they sell ad placement, not people.
It’s not the placement that’s the value that’s being sold, it’s watching the ads that is. So they definitely use your data to sell your attention, which is the currency you’re paying with.
Yes, it is ad placement that is the actual thing being sold. Advertisers hope to get something else out of it (usually sales), but what is actually sold is placement.
> So they definitely use your data to sell your attention, which is the currency you’re paying with.
No, they are selling the placement. The placement is valuable because, in aggregate, there is an expectation that a certain share of the people to whom it is shown will give some attention to it, but the advertiser generally pays by impression, not by seconds viewed × share of viewers attention devoted to the ad during that time.
But, in any case, either selling placement or attention is different than selling the user, which is a flatly inaccurate description used solely because of its emotional charge.