You can build an interesting profile of people by analyzing their purchases. Maybe it's right, maybe it's wrong, but it's certainly none of their business. If it's wrong, it could get you negative attention that's undeserved. I'm not particularly interesting, and my concern is mostly philosophical, but that's good enough. The only reason I need is cause I don't want to be studied. I don't give a shit about 25¢ off a bottle of seltzer water(store loyalty card), or cash back from some company for telling them everything I buy. I'll work for my money, and they can fuck off. Offer a product/service I'm interested in, at a price I find fair, and we can do business. No abstractions, and no hassle. You give me stuff, I give you money. Straightforward and easy.