[tuankiet65]

I used to resist getting a store card for this very reason, until I realize that they can track me through the credit card that I used anyway. This requires the self checkout machine to record the credit card number from the POS though - does the POS expose this information?

[im_dario]

The POS can store anything that can trace a customer. It wouldn't be hard to derive a unique token from the credit card information, so it doesn't have to deal storing anything sensible.