Very important point. In my workplace, often the smartest engineers are so focused on doing smart things, they forget that the data they're dealing with belongs to, or identifies, people.
Got to make those yearly objectives/appraisals count though.
Perhaps a more subtle thing for them to keep in mind: many people carry out a mix of card/online and cash transactions. Only the card/online transactions will be captured. The Panopticon's record will show an extremely unhealthy and meagre diet for me for instance because I buy fresh fruit/veg at markets - cash only.
It strikes me that data censored through transaction modality and then used to make marketing decisions may result in poor results.
If they can still make predictions based on a partial dataset it's better than nothing and probably profitable to use. Chuck some linear regression or similar at it.
Cash will be around for a fair time yet, but you have a point for any form of regular or recurrent expenditure. As the above pdf explains 'hoarding' of notes as a store of value seems strangely popular...
Got to make those yearly objectives/appraisals count though.