This is why I frequently swap bonus cards with random people on the subway :)

A serious question, though I assume that you were joking: is it more creepy to have your own actions tracked and accurately tied to you, or other people's actions tracked and inaccurately tied to you? Both sound pretty awful to me, but I think I'd prefer the former if those were the only two options.

What stops these guys from selling to all the major health insurers.

Been buying too much sugar? Dental insurance up. Too much butter? Health insurance up. Bought three times the median amount of headache tablets? That's a paddlin'. Bought more alcohol than normal? Car insurance up.

Opt out to keep off their radar? They assume the worst and charge you double?

I've heard stories of this happening (shopper club data -> insurance companies), but it's never been substantiated.

Example sentence from mid-naughts: "I've heard several stories of USG bulk tapping Internet interconnection points, but it's never been substantiated."

Thinking from first principles lets us see incentives and probable outcomes before they are "substantiated" (adopted by the media).

I personally don't think shopper data is affecting insurance policies quite yet. But the groundwork is there (Acxiom etc), and the "great" thing about data is it stays around forever!

I'd guess a timeframe of 10 years, but does it really matter as to when?

> What stops these guys from selling to all the major health insurers.

Is this a response to my comment? I would guess that the answer is "nothing but the temporary protection of the law", but, assuming that protection is eventually revoked, it makes it all the more worrisome for me to have a random stranger's data taken as my own.

In the UK we have a company called Boots which used to be a pharmaceutical giant and is now a high street toothpaste and moisturiser giant. At the counter, they always ask if I have a 'Boots card' (purchase tracking card). I say no, because I don't, and they are often confused - because it's weird to not only have presented one immediately, but to claim not to own one. I'm then told I can be given my 'points' on a receipt so that I can add them to my (non-existent) card later.

I'm not a tin foil hat type, but I really don't like filling my wallet with tracking cards and can't be bothered to claim the miniscule compensatory benefits provided in return for proffering my purchase (and also location, hygiene, etc.) information.

Saying 'no' is almost more hassle than simply submitting, however, which is probably exactly what the company would like to hear. Suggestions welcome for brushing off this nuisance without a) Avoiding their shops entirely (not practical) or b) Being rude to cashiers.

Sometimes I do use several bonus cards, when there's some significant benefit (say, sale-out only for bonus-card owners). Guilty that. But I do not use them often and of course I don't use my real name when signing up for it. Or if I do — only when I use my CC anyway, which is rare.

Surely if you use your CC one time with this card they have your real details. After that every cash purchase where you use this card is tied back to you. Not hard to believe they do this and you should assume the worst.

> every cash purchase where you use this card

When I pay with cash, I usually don't present a card as well.

I avoid these for sure. As you say the reward is nothing - they can stick it.