[queuebert]

Credit card companies have all of this data. They could track classes of spending and regress out rising incomes, age, etc.

[matt-attack]

I’m just how exactly does my credit card company know how much I paid for shampoo?

[brewdad]

Your retailer knows exactly how much you paid for shampoo. In most cases, they know it was exactly you who bought it. Data sharing agreements through direct or third parties complete the picture for both sides, retailer and card issuer.